Julio's death, in which he desperately clutches at Kate for help while being dragged from the window. Being Half the Man He Used to Be. His screams are still audible as she's ducking for cover, accompanied by horrific crunching noises.
The vocalizations of the shriekers are rather terrifying, as are the bellowing howls let out by the Graboids in their death throes prior to birthing the former.
At one point, our heroes come across a dying Graboid. Few scenes later we find out that it and its kin have been TORN OPEN, letting out three Shriekers each. The concept calls to mind skinned beans, and how there's always a few pods in each of them.
Seeing the Graboid's final moments and then its carcass was pretty disgusting and scary.
The fact that the Graboid species has that kind of brutality built into its very lifecycle is chilling in a way beyond standard gory murder, going into Alien territory.
Conversely, if one doesn't immediately suspect the dying Graboid had been torn open by its offspring, the alternative explanation that springs to mind at first glimpse of its eviscerated body is that another Graboid took huge bites out of it in an act of Monstrous Cannibalism. Which the third movie showed us can happen, at least between different life-stages.
The scene that starts this off is Earl and Grady following after a Graboid moving away from them, completely contrary to what they and the viewer has come to expect from the things. Earl's rather nervous and uneasy attempt to rationalize what's going on pretty well sets the tone for the remainder of the movie.
And for good measure, the Jump Scare of the Graboid suddenly above ground and right on the hood of Earl's truck! Yikes!
By extension, the entire night section of Aftershocks up to the Shrieker's reveal is one big chilling case of Nothing Is Scarier.
Particularly scary if you think about it long enough...but how close Earl and Grady were to the Graboid that split open is utterly terrifying, especially as Grady was on his way up to check out the worm right as its final bellowing cry came out...just how close were our heroes to getting eaten before they knew what was going on and sharing Pedro's eventual fate...?
The reveal of what became of Pedro, one of the plant workers. Earl and Grady wait for him to pick them up in his truck, but after seeing what became of the Graboid, we see the truck suddenly appear off in the distance and then suddenly stop. After a while, Earl and Grady head on over to see what's going on—finding the truck all chewed up. Grady spots a pair of hands behind the truck's cab, but then he sees that the arms are all that's left of Pedro. "Oh, God!" indeed.
There's also a pretty good Jump Scare while Burt's driving around at night. He stops to check his map and suddenly hears a noise on his hood. He looks up and sees he's surrounded by Shriekers. Smash to Black, as they scream.
The actual reveal of the Shriekers is something of a Wham Shot in itself as the camera, mirroring Earl and Grady's own expectations of something gigantic, zooms back out in preparation for the reveal and out comes...this squat, chicken-like thing about the size of a farm pig...which seems like Nightmare Retardant until you remember that that little thing utterly destroyed Pedro's truck, murdered Pedro himself, tore up the radio tower, and entered life by eating its way out of a Graboid. Suddenly, Grady's growing terror the following morning when he realizes there's 24 of the things unaccounted for left out there grows chilling....
