Nick puts the 20th tally on the jail cell wall representing his 20th minute in jail. In the next shot, the wall doesn't show any tally marks.
When the magnet picks up the car in the junk yard, the driver's window is halfway open. In the following shot of the car being placed into the crusher, the window is completely closed.
When Déjà Vu checks his big Rolex, the time in the closeup is 7:22, but in the wide shot, it's 7:17.
When Nick enters the first vent in his jail cell, the crowbar he used to open the vent is swinging in its rack. In the next shot, the crowbar is perfectly still.
In the first shot of the prison cell, a food processor and its parts can be seen on the shelves. These are gone in subsequent shots.
When Dr. Flammond tells Nick that the weapon has to be completed by Sunday, indicating September 24 on a calendar, Nick replies "That's Simchat Torah!" Simchat Torah is a festive Jewish holiday in which the liturgy includes reading the last portion of Deuteronomy, the final book of Moses, and then beginning the cycle again with the book of Genesis. In 1984, Simchat Torah fell on October 18. Furthermore, September 24 hadn't fallen on a Sunday since 1978 and wouldn't again until 1989, and neither of those dates coincide with Simchat Torah.
In the opening credits, the surfer/shooters are shown riding to the beach in a 1937 Ford Woody. The lyrics, however, refer to a Chevy.
When Nick enters Dr. Flammond's cell and Dr. Flammond is seen emptying spoonfuls of dirt from under his cot, it can be seen that he is scooping dirt from a different pile underneath the cot rather than the tunnel he is nearly completing.
When Hillary is riding the motorcycle to get Nick at the lake (long shot as she is driving down the road), the helmet strap can be seen going down the side of her chin to hold on the messed up "hair".
Obviously, Nick Rivers' thumb isn't touching the guitar strings.
"Der Pizza Haus" is just one of the numerous translation errors of English words and phrases into German. This is also the case with almost every German dialogues throughout the movie. Lots of words don't make sense, grammar is way off and some lines are even gibberish.
In the "Pizza Haus" dance, when Nick (Val Kilmer) runs up the wall and back flips, the cable of his trapeze rig is visible.