In the "save the clock tower" sequence, the same man rounds the corner in the background twice in the same direction.
When Doc is telling Marty how his time machine works, he says, "Never mind that now, never mind that now." When he says this, Marty has the camera down by his side and isn't filming, yet later in the film when Marty shows the film to Doc in 1955, the film starts out with the camera on Doc saying, "never mind that now, never mind that now..."
The "Save The Clock Tower" flyer that Marty shows to Doc Brown in 1955 is smooth and pristine when he first unfolds it; in later shots it alternates between being wrinkled and smooth before Doc Brown wads it up.
When the lady from the Hill Valley Preservation Society hands the flyer to Marty, the text that Jennifer writes on its back later is already visible.
When Marty is showing the tape to Doc in 1955, 1985 Doc (in the recording) says his line about the 1.21 gigawatts of electricity needed. When the Doc of 1955 says "what did I just say?", Doc in the recording is still talking, but when the tape was recorded, Marty is talking about plutonium immediately after the gigawatt line.
When Marty is getting ready to play guitar through the huge amplifier in Doc Brown's house, he switches on the amplifier, turns all of the gains and overdrive up, plugs the cable into the amplifier, then proceeds to plug the other end of the cable into the guitar. The moment the cable touches the guitar's output jack should have been the moment the speaker blew up. Most guitarists will plug the cable into the guitar and amp, THEN turn the amp on. Doing so will avoid making all of the noise that results from the cable and guitar jack making contact.
An episode of "The Honeymooners" did actually air on November 5, 1955. However that episode was "The Sleepwalker", not "The Man From Space". As mentioned in the Anachronisms section of this page, "The Man From Space" aired on December 31, 1955.
Much lighter items than Marty are not blown backwards by the speakers.
When Doc loads the DeLorean up with plutonium, he uses what appears to be a glass tube that has a red liquid in it that's supposed to be the plutonium. Plutonium is not a liquid, and it's not red; it's a bright silver/gray metal that quickly oxidizes to brown/black and becomes flaky when exposed to air.
During the Twin Pines Mall scene, Doc has the remote control and does what is called 'power braking' which allows a driver to maximize the torque in the torque converter. The car does not move but the tires spin. This scene makes you think that the DeLorean is actually building up mph, but really the car is only building up torque (rpm), just like drag racers do. When Doc releases the brake control for the car, the display should read 0 mph not 64.8.
After Marty gets back to 1985 and sees his parents, they don't say anything about how much he looks like Marty from 1955. However, this obviously isn't the first time they've seen their son. They may have noticed the resemblance and may have mentioned it earlier. Alternatively, there is no reason to think they would notice how their son looks like a person they met 30 years ago for one week who they never saw again after that and whom they have no photographs of. Also, despite feeling that "Marty" is a beautiful name, Lorraine wasn't sufficiently motivated by this fact to give this name to her first son (David).
When Doc is walking across the ledge of the clock tower when the camera is looking up towards the ledge, you can see that the section Doc breaks off is clearly marked (it's darker than the rest of the ledge). However, this just indicates that the ledge was in disrepair and only adds to the believability that it would crack under his weight.
Marty went to the past wearing Nike sneakers. When he was being chased by Biff he was wearing Converses. Then when he went back to future he was wearing Nikes again. Marty brought no other clothes with him, but it's conceivable that he obtained a pair of Converses with his other period-correct clothes.
DeLorean speedometers only go up to 85 miles per hour, but the one used in the movie goes up to 95 miles per hour. However, Doc presumably "doctored" it.
In the dinner scene at Lorraine's house in 1955, Sam says he's never heard of John F. Kennedy. Even though Kennedy was not yet the President, he still would have been known because he was a United States Senator in 1955, a United States Representative before that, and for his exploits in the United States Navy during WWII. Even so, there is no reason to assume that Sam would have been aware of this or cared.
When Marty is being chased by terrorists, Eric Stoltz is playing Marty. Michael J. Fox was later chosen over him, but they kept the driving scenes at the mall with Stoltz in, since the shots were fairly distant and the driver's face is not particularly visible.
When Marty looks up Doc's address in the phone book in the diner in 1955, the close-up shot of the hand scrolling the page is clearly that of an older man with age spots, and not the hand of someone of Michael J. Fox's (or the character Marty's) age.
When doc is using the remote control for the time machine at the start, a close up of the remote control shows that the voltmeter for the battery is reading zero - the unit is off.
When Marty and Jennifer arrive late at school, you can see through the windows at the end of the hall that it's dark outside.
In 1955, when the DeLorean is approaching the wire to receive the 1.21 Gigawatts from the lightning bolt, the Flux Capacitor starts to work, spreading the tell-tale blue flashes of light around the vehicle, yet the Flux Capacitor has not received any electricity from the lightning yet.
At the beginning of the film, in the kitchen Biff goes to the refrigerator to get a beer and complains that all George has is Lite beer. There appear to be 3 cans of Budweiser on the fridge door shelf.
When Doc shows Marty the diagram of the famous "Flux Capacitor", you can clearly see that it's actually labeled as the "Flux Compressor".
When Marty asks Doc, "does this run on gasoline?" he explains it needs something with more kick: plutonium, however in Part III Doc tells Marty that the plutonium is for the flux capacitor, but the car itself runs on ordinary gasoline.
When Marty takes 1955 Doc to find the Time Machine, he said that the starter isn't working right. It is true that the early model DeLoreans are notorious for having faulty ignition systems. But Marty is supposed to be under the notion that the Time Machine ran on plutonium and not gasoline (as he asked a question regarding to how the Time Machine worked to the 1985 Doc earlier in the movie) and he looked back to find that the plutonium chamber was empty, so he should believe that the DeLorean had no power due to being out of plutonium. He wouldn't be made aware that the DeLorean also ran on gasoline until Doc and Marty prepare it for the jump back to 1985.
When Marty returns home after departing from Jennifer, he rides his skateboard in to Lyon Estates. The signs for the Estates are in the road rather than on the sides of the road (and they are blocking the stop sign), this is because of a need to make a tighter shot for the viewer.
The Man from Space (1955), which Lorraine's family watches on November 5, 1955, wasn't shown until December 31, 1955.
Ridiculing Marty's jacket, Skinhead in 1955 refers to Marty as "this dork." The word "dork" as a name for a stupid person first appeared in 1967.
During the clock tower chase, disability signs are visible. These were first used in the 1970s.
The guitar Marty plays in 1955 is a Gibson ES-345 with a retrofitted Bigsby vibrato (you can still see the studs on which the original stop tailpiece had been fitted); both the guitar and vibrato were introduced after 1955. The ES-345 was first produced in 1958 and it uses humbucker pickups invented by Seth Lover of Gibson in 1957.
In 1955, the record shop has Chordettes record sleeve art used on a CD from the 1980s, and Eydie Gormé's album 'Eydie In Dixieland' from 1959. There's also Patti Page's album 'In The Land Of HiFi' (1956) and 'Nat King Cole''s album 'Unforgettable' (1954), the only record released before 1955.
When Marty watches George ride his bicycle past Lou's diner, the bicycle bell is rung several times. There is no bell on George's bicycle (even clearer later when we see the bicycle leaning up against the tree).
The sound and volume of Marty's singing never changes, even when he moves way back from the mic.
When Marty hits the final note of Johnny B Goode, you can hear the note being sustained with vibrato, yet Marty isn't applying any.
When Marty is playing "Johnny B. Goode" in the dance, George pushes the guy dancing with Lorraine aside yet has not kissed her. Marty takes his hand from the fretboard, yet the sound of a guitar strumming can be heard even though Marty is the only guitar player on stage.
When Marty plays "Johnny B. Goode", the double bass sound is the sound of a slapped double bass (the string pulled and knocked on the wood to give it a percussion effect), while the musician plays normally with his fingers. At the end of Marty's solo, the drums can still be heard, but a shot of the drummer shows that he is not playing the drums.
When Marty is waving to the girls in the aerobics gym (which used to be Lou's Diner) the camera truck is reflected in the large window.
In the parking lot at the mall, Doc uses a remote control to drive the car after putting Einstein in the driver's seat. As Doc backs the car away from himself and Marty, the stunt-driver's hands wearing black gloves can be seen turning the wheel from underneath a dog suit.
During the first time travel experiment in the mall parking lot, when the DeLorean reaches 88 miles per hour, it is shown beginning to glow and throw blue sparks. As it does so, it drives past crewmembers with lighting equipment and a generator.
Right before the DeLorean makes contact with the wire to send Marty back to the future, you can see another person sitting in the passenger seat of the DeLorean.
Reflected in Marty's sunglasses after he is thrown across the room by the speaker.
At the end, when the McFly family rushes outside to get a look at the "wrecked" car, they encounter Biff polishing the car. In the background, the street is shown to come to an abrupt end, clearly showing a large commercial building where the street comes to a "T." All other shots of the street where the McFly family lives show a long, residential street that doesn't end.
After Marty arrives in downtown Hill Valley in 1955, you can see some road markers on the side of the road behind him. These markers are for US Highway 8 and US Highway 395. While US-395 does pass through the state of California, US-8 does not and never had, even back in 1955. US-8 runs through the states of Michigan, Wisconsin, and Minnesota.
After Marty arrives in 1955 early in the morning and leaves the barn, he drives what should be a short distance but when he arrives in front of his neighborhood the sun is quite high in the sky. Although we were never told the distance between the mall (Formerly Peabody farm) and Hill Valley, Marty went to the Twin Pines Mall on his skateboard in a matter of only a few minutes in 1985.
The alarm clock in the car goes off at around 10:03, and it takes Marty the next minute to accelerate the De Lorean to 88 mph. That means the start line would have been about a mile away, clearly a far greater distance than from where he actually starts the car.
In the town square, there are highway signs indicating US 395 and US 8 are nearby. Though the former is a highway that runs from Canada south through Washington, Oregon, California, and Nevada, US 8 is nowhere near California; it runs from Minnesota to the upper peninsula of Michigan, through Wisconsin.
When Marty returns from 1955 he goes to Lone Pine Mall and sees himself doing the exact same thing he did before he went back to 1955. The chances of the alternate Marty behaving the exact same way he did in the original timeline are astronomically low considering this Marty is a completely different person who was raised by two loving parents who were happily married.
Marty looks up Doc Brown's house in the phone book and asks Lorraine's parents where the street is. Once Marty arrives at Doc's house he notices that the garage is the same as it was in 1985, so he should have known exactly which street it was on.
How many Marty McFlys are there? The "original" Marty sees the Marty (Marty II) raised by the different George McFly go to 1955. Marty II wouldn't use a skateboard, since he has a Toyota 4x4. Presumably, Marty II would also return to 1985, meaning two distinct Martys exist in 1985.
Marty carries around a photo of his siblings and the people in the picture slowly fade. However, the photo never should have existed if Marty was going to fail and it should have disappeared instantly. Marty should instantly disappeared because he never would have been born. However, since he does succeed in the future it means that the photo never should have faded and Marty should have never started to fade.
After returning to 1985, Marty finds a new truck, his brother and sister successful and wearing better clothing. His parents come in from tennis and are swanky upgraded clothing also. His dad has multiple successful books that he wrote, but the kitchen hasn't been upgraded even though the living room has been changed to upgraded furniture.
Doc Brown considers traveling to the birth of Christ, which he enters as "DEC 25 0000". There is no year between 1 B.C. and 1 A.D, and it is also believed that Christ was actually born in Spring or Summer of 6 or 4 B.C. (although Robert Zemeckis has claimed that this was meant to be a joke). Furthermore, the DeLorean would still have arrived in California in the "year 0000" with no way to get to the Middle East.
When Marty wakes up in his bed in 1985, in the bookcase behind his head there's a yellow magazine named "RQ". This stands for "Reference Quarterly", a trade journal of reference librarians. In the DVD commentary track by producers Bob Gale and Neil Canton, they admit that the set dresser made a mistake in putting it in, as a teenager would have no reason to have a copy of "RQ".
At the diner in 1955, Marty wants something without sugar but asks for a "Pepsi Free." In 1985, Pepsi Free was the name of caffeine-free, not sugar-free, Pepsi. If Marty wanted Pepsi without sugar he should have asked for "Diet Pepsi" or "Diet Pepsi Free." Presumably the filmmakers ignored this in order to get both the "Tab" and "Pepsi Free" gags into the scene.
Marty tells the band at the dance that the song is in B, but when he plays, it's in B flat. This was a popular key in the fifties as it was easier to play in that key on a saxophone. Once rock bands dropped saxophones in the sixties, the most popular key was A, as it is easier for guitarists.
The "Libyan" driver wears a Saudi headdress.