Revealing mistake: During the disco scene, Elaine is dancing with a fisherman who was just stabbed in the back. The fisherman has a knife sticking out of his back and you can clearly see the block that the knife is stuck in protruding from his shirt. There are holes from other takes too.
Revealing mistake: When Elaine is visiting Ted at the mental hospital and she says Lt. Zipp died this morning, when Ted picks up the water right before he spits, there's the same amount in the glass when he picked it up and set it down. So he didn't drink anything or spit any water.
Revealing mistake: In the flashback scene in the bar, one of the girl scouts slams the other girl scout onto the floor and one can see the mat that the girl lands on. It had been covered in dirt or dust but when the girl lands it is swept away and you can see one of the corners of the mat.
Revealing mistake: Throughout the cockpit scenes, Otto's (the auto pilot) face is just painted, with no facial features sticking out. When he is about to fly the plane, he winks out the window, and turns his head. After he turns his head you can see the extra attachment on his left eye used for this.