Continuity mistake: When the shark slams into the cage and makes Hooper drop his weapon, it shows the underside of the shark; look at the its mouth. When the shark is about to slam into the cage again its mouth isn't the same size as it was before. You can tell that they used a real shark when they showed the underside. (01:54:15)
Continuity mistake: At the end Brody throws the diving tank into the shark's mouth with the bottom first. When he shoots the tank it has turned round with the fat end facing out.
Continuity mistake: Before Alex Kintner is attacked, Sean Brody is shown sitting on the beach singing. After Alex is attacked and people are running out of the water, Sean can be seen standing on the beach, and in one shot, Chief Brody can be seen grabbing him. But a couple of seconds later, Sean is shown sitting on the beach in the same spot he was before, as if he hadn't moved. (00:16:55)
Continuity mistake: When Jaws leaves the pond after the attack its fins go below the water as it approaches the bridge, the scene immediately changes to the bridge, the woman is shouting "shark" and we see the fins go below the water again.
Continuity mistake: When the man gets attacked the long shot shows two of the three boys on top of the upturned boat, then we see the leg sink to the bottom with a trainer on, even though the man was bare footed. Then the camera passes the boy in the water and the other two boys are only just climbing up onto the boat.