After the power goes out the first time the microwave clock is still going.
When the boys are about to get hit by the truck, the view through the window behind them shows the car is moving when it car is supposed to be still.
In the final scene, Max Minot's swim trunks alternate between tan and dark green.
The duct tape around Bartolucci changes its position almost from camera shot to camera shot.
The first time the phone in the house is used they make a big issue to keep it on speaker, the next time, on even a more important call, it's not even bought up and not on speaker.
In the casino scene, one of the characters talks about going over to the sports book. There is no sports betting in New Jersey casinos.
In the last scene the pinky on Bartolucci's right hand is back. It was kept on ice throughout the movie and given back to him at the end, then sewn back on.
SPOILER, near the end of the film, after Jeckyl and Heckel are shot and killed, there is a close shot of Heckel, and although he is supposed to be dead, it is noticeable that he is breathing.
Ira brings brownie mix from Ralphs, a California chain of supermarkets; the movie is set in New York.
When Heckle and Jekyll are making the deal with the mystery person, the big balloon in the background says on it "Mountasia Family Fun Center" which is in Valencia /Santa Clarita California, not New York.
At the end, when Max is giving directions to Montauk, Long Island, He says take Parkway Central and Central Park Expressway or the Southern States. There is no Central Park Expressway or Parkway Central in the Tri-State New York Area. There is a Grand Central Parkway.
The queens midtown tunnel connecting Manhattan to Queens is a two lane tunnel in both directions, not a four lane tunnel as depicted.
Reflected in the mirror when the gang are debating how Charlie should go to the bathroom.