Garbled and unintelligible lines
Loved Jaws my whole life. One of the distinguishing features that's always tickled me, that I'm certain was a stylistic choice, is the amount of garbled or unintelligible lines of dialogue there are.
Sometimes they are caused by overlapping dialogue, walkie-talkies, the mannerisms or emotion in the delivery, the intentional sound design and mixing, or just the accents.
Obviously the opening scene sets the trend. You could just assume that Chrissie is not really verbalising but if you listen closely (and spend forty odd years leaning in to the speaker and spending lots of money on ever improving home video releases) you can just about tell that she's saying actual lines like "Oh God it hurts."
Other notable instances are :
Hooper's pretzel stuff mouth during the night-time discover of Ben Gardner's boat. "You don't say. Wanna pretzel?"
Another favourite of mine is the one right after Quint and Hooper try to snag the first barrel and tie it on, but the shark leaps out causing them to lose it. Quint says "Haul in the line or it'll foul us." It took me decades to pin that one down.