Fridge Logic: The scene after Hooper is shocked into dropping the huge shark tooth by the severed head in the hull of the boat consists of him and Brody confronting the mayor and demanding the beaches be closed. The mayor takes the absence of the tooth as the lack of evidence he needs to ignore their warnings - the two of them seem to forget they actually have stronger evidence in the form of the mutilated human remains aboard the wrecked boat! The reason for this gaping error is that the shot of the severed head was added by Spielberg at the last minute to wring "one more scream" out of the audience, but no script alterations were made to accommodate it.
The first shark victim wasn't enough evidence why should a busted up boat and a busted up body inside be proof of a shark to the mayor?
The mayor still hoped the (dead) tiger shark was responsible
The scene where Hooper dives into the water seems not-so-scary until the reveal of Ben Gardner's head, since he knew that the shark was not in the area due to his boat's radar. Until you realize that Brody doesn't know how to operate any of the gear and couldn't warn him if the shark did start to return.
Fridge Horror: When you realize that Pippet the dog was probably eaten by the shark.
This troper took that as a foreshadowing that the shark was in the area.