For me, Marge struggling to get back up on the boat, only to have the shark suddenly appear under her and CHOMP! The shark looks like it's smiling just before the attack, so creepy and intense.
Yes, that's a good one. But my favorite is when the shark grabs Eddy and swims with him in its mouth, rushing toward the side of the boat, smashing Eddy full-frontally into the hull. I thought it was ghastly when I saw it in its first theatrical release, and I still think so every time I see it...!
Marge getting eaten was the most intense moment for me. The helicopter attack just happened, so the intensity level is already amped up. Marge is struggling and fearfully pleading for help, and when you see the shark gliding just below the surface toward her--mouth open and ready to claim her--you know she's not going to make it. My heart sank a bit at that point. The shark rises up behind her out of the water, and we see just how massive it is compared to her. Its ascent is smooth, effortless, and even graceful, while she is flailing and struggling helplessly--such a difference in experience. Then, you see its nose sharply thrust downward as it bites down hard on her, leading to the most intense moment of the segment for me--the chilling sound of her bones getting crushed, revealing just how powerful and destructive the shark's bite was. The shark appears to bite down again, resulting in another crackly crunch. She has most likely been killed by this point--mercifully--and the shark disappears below the surface with her body in its mouth to be eaten.
The camera angle of the attack largely leaves it to the imagination to decide how the shark took Marge in its mouth as it ate her, leading to gruesome speculation--feet first, head first, folded in half, etc. Despite being bloodless, her death seemed disturbing because she was a kind and nurturing character who is swiftly and easily overtaken and brutally crushed to death with a couple of quick, devastating crunchy bites. She was just obliterated. It seemed unfair, and some of the intensity in the scene is the recognition of the fact that nature often is brutal and unfair. The shark cannot and does not care who she is.
Eddie's death is also intense--especially when he gets violently slammed into the side of the boat and yanked down moments later--but I found it less intense that Marge's death because less is shown of the shark during the attack.
I also liked the scene when Chief Brody, his wife and the deputy find Tina curled up in the boat, and she is so beside herself with fright that she can't get the words out to tell them what happened, then she finally screams "SHAAAAAAAAAAAAAARK!!!!!!!!" She is the first actual witness to confirm what Brody knew all along. I thought that scene was very moving.
That's my favorite non-shark scene in the movie, Mystery. Ann Dusenberry doesn't seem to be acting when she comes out from her hiding place.
I also love the "Somebody look out for Mike!" scene. Genuinely edge of your seat when Timmy and Paul are trying to get him out of the water as the shark approaches. It looks terrible when it lunges past the boat, but the build-up is great. JW'S music is perfect, too.
Don't forget the menacing gut wrenching scream from Jackie in the distance while the shark is coming along with the score working with her scream. Then ofcourse showing Sean & Jackies face in horror it truly gives you a glimpse of how horrifying it was from their angle. People always forgets that part because they are annoyed with Jackies screaming but I always loved it.