Visible crew/equipment: After Brody buys the sign supplies, when Hendricks shows up Brody places the box in the front seat, and as Hendricks tells Brody about the Boy Scouts, pay attention to the left window across the street, where we can see one of the local residents holding a camera and looking out the window facing the location shoot, taking pictures of the actors and film crew. The filming took place at the corner of Main St and S. Water St, Edgartown. (00:10:50)
Continuity mistake: When Brody sits on the beach watching the crowd in the water before Alex is killed by the shark, he wears a watch on his wrist which disappears a few shots later when he believes he saw something. (00:14:48)
Visible crew/equipment: Aboard the Orca, Brody accidentally causes the cage bars to fall over, and as both air tanks roll forward the multiple head set lights are reflected on the two tanks. (01:13:35)
Continuity mistake: At Orca's bow, the hole in the steel hull beside its number, is oval shape. However, after Quint is gone, when the ship begins to sink, and later when Hooper surfaces beside the wreckage of the bow, the shape of the hole in the steel hull is completely different! The white water stain lines change throughout the shots as well. (01:25:00 - 02:01:10)
Continuity mistake: At Quint's, when he holds the two steaming shark jaws, assorted dry goods on the shelves above the stove are seen, particularly the cans of Del Monte vegetables. When Quint gives Hooper the rope to tie the knot, some of the goods on the bottom shelf and every can of veggies on the top shelf are entirely different. (01:07:00)
Visible crew/equipment: In the scene where Quint shoots the shark with a harpoon gun, when the harpoon hits the shark you can see the shadow of the cameraman. (01:39:25)
Character mistake: During one of the shark scares at the beach, Chief Brody is running along the shoreline telling everyone to get out of the water. There are several frames where the Chief and a man with a moustache are at the water's edge. If you look closely you will notice that the man is smiling and laughing and other people laugh as well. (00:17:30)
Answer: Possibly a scar from having his appendix removed, I've been told.
The appendix shot is Brody - he is feeling inferior as the other two share tales of the sea and the only scar he has is from his appendix being removed.