Continuity mistake: At the beginning of the film when the shark attacks the divers, you see in one shot that the shark already had a burned scarred face. The shark doesn't get set alight until later in in the film. This scene was one of the last ones to be filmed.
Continuity mistake: In the scene where Chief Brody comes home drunk, Deputy Hendricks comes over to express his sorrows. When he's leaving/already left, Both Ellen & Chief Brody comment on Hendricks as "Poor Jeff." In the first Jaws film, Brody calls him Lenny. Jeff is actually the first name of the actor who played Hendricks.