Revealing mistake: During the naval battle, after an underwater shot of a man being eaten by a shark, check the poop deck on the left, and you'll notice a bulky floor with wrinkles around where people fighting and falling bounce on, revealing a tarp hiding a safety mat.
Revealing mistake: When Cassie's cab passes the truck and crosses in front of it while heading to the diner, skid marks from previous takes are visible on the road to the right of the truck.
Revealing mistake: In the first scene, they skid around a corner; there are many other skid marks on the same corner from previous takes.
Revealing mistake: When Gary is being interviewed at the end, Slimer and the Dragon fly over them and away. However, Gary keeps staring at the entrance door; seemingly, the cue didn't work here. A shot later, from a different angle, he is suddenly looking ahead.