Visible crew/equipment: When the man is in front of Brody talking to him on the beach the film crew are reflected in Brody's glasses.
Visible crew/equipment: When the first barrel goes on and Quint is at the front saying "5° port now." When we see a close up of the barrel at the bottom right of the picture you can see the wake from the camera boat. The wake is going toward the shark and not away from it.
Visible crew/equipment: As Hooper says the shark is "back for his noon feeding", you can see the camera and lighting reflected on Brody's glasses.
Chosen answer: As mentioned in the movie, the posion was in the needle and the shark's hide was too tough for the needle to penetrate. Hooper had to go in the water so that he could get the needle into the shark's mouth, where the flesh was less tough.
Kevin Howard