This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Carnosaur
Even with the ridiculous premise and some of the stiffest, most unconvincing dinosaur effects ever not to be produced by Syfy, the first film is still a very moody, very ominous, very bloody piece of work.
The scene where the Deinonychus finds a group of hippies who chained themselves to bulldozers and viciously mauls all of them. What's worse, all of the group could hear their friends being torn apart but are both completely unable to help them or free themselves to get to safety. The thought of being trapped in an isolated area with a monster ripping your party apart one by one while you can't get away is genuinely terrifying.
The death of Sarah Rawlins in Carnosaur 2. Most of the character deaths happen via a Gory Discretion Shot but for Rawlins we see it in fully graphic detail. After she's dragged out of the elevator by a deinonychus, Rawlins is thrown against a wall, where the dinosaur proceeds to slowly bite her arm off, exposing strands of muscle and bone. She's then finished off when it bites into her stomach and eats her innards as she coughs up blood and spasms to death. Of all the ways to go out, this was a really horrifying and Cruel and Unusual Death.