Why rated R?

I don't think the language was that bad. My only guess is when the dude gets his arm bit off

Nudity. There are three nude sharks the whole movie.

It's an R all the way.

- Stellan Skarsgard getting his arm bitten off and his bloody stump pumping blood, then the look on his face when the shark throws him into the control room window
- Michael rappaport getting ripped apart in a frenzied way with the camera lingering on his severed leg twitching
- the blonde woman getting dragged under water and emerging in the mouth of the shark and the screams as they attempt to save her
- Samuel L Jackson in the big sharks mouth and the smaller shark coming and ripping off a chunk

The key thing about these killings is the tone. Jaws is a fun, aquatic adventure movie, so the killings may be brutal but fit the overall themes. Meanwhile, Deep Blue Sea is more cold and mean spirited in its tone, and the killings feel much more disturbing as a result.