This is based on opinion. Please don't list it on a work's trope example list.
Spoilers abound below...beware!
- Miss Burke's decapitated head sprouting tentacles, then crawling back to and reattaching itself to its body, which is still walking around.
- Principal Drake getting up after being shot, with a bunch of little parasites crawling out of the bullet hole in her head.
- Ditto her Impaled Palm and subsequent chase through the darkened school by the coach.
- Marybeth's transformation into her alien form, her arms turning into Combat Tentacles and her head melting into her body, then turning into one ugly creature that looks like the Predator's deformed cousin.
- The sight of Jon Stewart with a pen jammed into his eye is either this or Funny Moments.
- Mrs. Brummel in the shower with her skin peeling off, and moaning for help. Made even more gruesome when patches of hair come away, with mushy scalp included.
- Coach Willis standing out in the rain with dozens of little tentacles sprouting from his head and razor sharp teeth
- Delilah's face with parasites crawling around inside.
- The parasites crawling into Casey's face slowly as he screams and the Queen inches from his face.
