Whenever Roger enters his Aunt's bedroom to look at the closet the window of the room is reflected in a mirror and it is clearly day time when it should be night... this happens on occasion throughout the film.
When Roger and Jimmy are surprised by Skeleton Ben at the front door, their clothes and hair are dripping wet. Two seconds later, their clothes and hair are perfectly dry.
The rope that Roger lowers into the "black hole" in his medicine cabinet is a smooth, cotton rope. The rope that we see him sliding down is a rough, hemp rope.
When Roger and Chet Parker comment on Aunt Elizabeth's picture which is covered partially with a rug, the rug changes position several times during cuts.
When the grocery boy walks up the porch to knock on Mrs. Hooper's door, the sun is shining on the backside of the house. When it cuts the sun is suddenly shining on the front of the house, hitting the door.
When Sandy is shot with the shotgun there is no blood anywhere on the porch or near the door.
When Big Ben is talking, you can see the actor's mouth move under the skeleton make-up.
In the bathroom, as Roger bends down to pick up the stool to break the mirror, you can see the wall move slightly as the "cabinet" behind the mirror is removed. It's most obvious if you watch the reflection in the mirror.
When dog escapes with a ghost/demon hand in it's mouth, its obvious that somebody called him to come because he looks to that direction and then goes.
During the Vietnam flashback when Ben is firing the M60, there is no bandoleer loaded in the gun and there are no spent shell casings being ejected while he is firing.
When Harold calls the cops. they arrive too soon. It would take them much longer to come after being called.
When Roger enters the room armed with a shotgun to shoot the stuffed marlin. You will notice a crew members entire arm (and wrist watch) in the scene to his left. The crew member is most likely holding a boom mic, although it's not entirely visible.
When Roger is trying to type on the computer, he turns the television off and the camera crew is clearly visible in the reflection of the TV.
At 27:50: When Roger turns from the closet and says, "I must be going crazy!", as he walks away, you can see the boom mic arm drop down to create a shadow in the moonlight from the window.
When the cops arrive an officer says, 'I know you, right? You're Roger... ' you can see the boom mic reflected on the visor of his police cap.
In one of the first scenes in which Roger is inspecting the haunted closet, he turns and leaves the room and a moving boom mic's shadow is clearly visible in the upper left hand corner.
One hour and one minute in, while Roger is babysitting, he is also watching a show with his ex-wife Sandy in it on TV. Her character says to another in the show on tv "My sister is an only child and you abused her". Your sister would not be an only child if she was your sister, as you would be her sibling, meaning not an only child.