The projectionist in the movie theater complains that it's getting hot in the projection booth, indicating that the air conditioning was working but has stopped due to the Blob blocking the shaft. But the Blob is vulnerable to cold, and should have avoided the cold air blowing in the shaft.
The visiting team has 12 men on the field in the football game in the opening scene.
Just before the final battle against the blob, a manhole cover on the ground can be seen, heavily deformed. But manhole covers are made of cast iron, which is rigid and fragile, so it should be shattered to pieces instead of being deformed.
Dr. Meddows says that outer space has mutated his "bacteria." But then he adds, "Our little virus has grown up." Yet bacteria and viruses are two entirely different things.
After Paul's arm is torn off and hits the floor, a small rise is visible for a brief moment near the wrist where the actor's real arm goes through the floor.
When Meg and the two boys are running to leave the theater in front of the movie screen, the boy in the yellow sweater is laughing, when he should be terrified.
Because of the highly corrosive acids The Blob uses to dissolve its prey, there should be some kind of trail of acids it leaves behind where ever it goes. But not so much as a drop of it is shown throughout the movie. Instead, it seems to leave no sign of it in its destructive wake.
When Candy Clark is bringing dishes back into the diner kitchen after trying to unclog the sink and she sees the cook being dragged into the sink, the crew can be seen in the reflection on the swinging door's window.
When Meg and the two boys are running to leave the theatre through the side exit, you can see the Steadicam operator's shadow on the door they go through while the projector is flashing.
When Dilon's characters goes out from the police station, the shadow of the camera is clearly seen (minute 37).
Reflected on Scott's helmet at the beginning of the movie when Paul sits down next to him
After the blob devours Paul, right before Meg ends up ripping off his arm, it for some reason spares Meg instead of latching on to her and devouring her, too.
When Meg gets out of her car to talk to Brian as he's walking down the street at night, the head of a boom Mic is reflected on the window of the china shop at the far left of the screen just before the camera stops moving backwards