That's not even the most fucked-up part! As Rocky struggles in the harness, screaming for help, we watch the blind man cut an opening in her pants with a large pair of scissors and approach her with a turkey baster. His disgusting plan becomes clear: with his daughter's killer dead, he's now going to impregnate Rocky to "replace" his dead daughter. He even has a deranged justification for his actions: "There's nothing a man can't do once he accepts the fact that there's no God."
Luckily, before he can insert the baster, he's attacked by a mallet-wielding Alex, who was actually alive the whole time. (In one of the film's slightly confusing twists, he tricked the blind man into thinking he killed him with the garden shears.) After Alex restrains the blind man, he frees Rocky from the harness. Shaking with rage, Rocky plunges the baster right into the blind man's mouth and squeezes tight. It's even grosser watching it.
The audience I saw the movie with went nuts at this part. There were screams. There were gasps. There were even some horrified laughs. As Jezebel's Rich Juzwiak points out, the moment probably owes more to subversive movie king John Waters (Pink Flamingos) than modern scary movies like Paranormal Activity, Insidious, or The Conjuring. Rocky, a classic "final girl" in the horror-movie tradition, turns her evil attacker's phallic weapon against him, and provides the movie with its most cathartic (and gag-inducing) scene.