Continuity mistake: When Ellen is on the boat, and sees the shark coming towards her, the distance between her and the shark does not look very far. When it cuts to Mike, Jake and Hogie in the plane, from their view the distance between the boat and shark looks much greater, about 60-70 metres. Also, only about five seconds later, the shark jumps out of the water and strikes the boat, the shark could not have swam that distance in such a short time.
Character mistake: When Polly answers the phone and is told of the log drifting in the channel, she immediately yells to Sean and tells him this. However, she does not leave enough time for the caller to be able to tell her all this, she leaves 1-2 seconds before passing it on to Sean.
Revealing mistake: In the scene where the shark has Michael cornered in the old, rusted boat; as he's about to use his oxygen tank to rocket up to the surface, the shark breaks through the wall and when it does, a large number of thick tubes can be seen running into the shark to make it work.
Factual error: The shark that attacks the Brodys in the Bahamas is presumably the same one that kills poor Sean Brody on Amity Island (that poor kid can't catch a break). Ellen departs for the Bahamas after Sean's funeral and the shark follows shortly thereafter. So, the shark swims from Amity, an island off the North Atlantic Coast, down to the Bahamas in order to stalk Ellen, Mike, etc. in a matter of days. Hmmm. As Matt Hooper said in the first film, "fast fish".