Revealing mistake: At the beginning when the ruler is making his speech, you can see his modern day fillings in his upper molars.
Revealing mistake: When Bill Murray is blowing up the prison door, you see the explosion, but the explosive is still intact.
Revealing mistake: When Norman and Billy crash the boat, the side panel rips off of it before they hit the rock.
Revealing mistake: When Foyt wants to put the GMC van into neutral at the police roadblock, you can see the cable towing the van towards the police car. (01:03:30)
Revealing mistake: While the two dudes are talking up about getting girls, the couple behind them appears to be making out - but the girl's face is resting into the guy's shoulder while his head moves about. (00:19:31)
Revealing mistake: In the letter to Mike Gallagher attached to the newspaper, subscription is misspelled. Sally Field is a reporter, so she should have caught that. (01:19:43)
Revealing mistake: The first time David werewolfizes, we're treated to the complete process... hair developing, bones painfully lengthening and twisting... and the torso of the actor very visibly halfway in the floor while all this is going on to the full-body werewolf prosthesis. Oh for computer graphics at the time to erase that detail of the process.