- Alternate Character Interpretation: Billy is subject to this since we know so little about him. His ranting during the phone calls indicates that he had a very negative experience with a person named Agnes and a baby, but nothing is known beyond this. There's also the question of just how insane he actually is (several time he acts in such a way that indicates that he knows what he's doing and is acting with premeditation) and whether or not the phone calls are just an act to intimidate his victims or if he really is just that crazy. There's also the question of how he's able to change his voice so often.
- Cult Classic: Considered one of the grandfathers of the slasher genre. Its cult status even gained it a 2006 remake.
- Ensemble Dark Horse: Barb is fondly remembered thanks to Margot Kidder's performance.
- Funny Moments: Mrs. Mac is discussing with Clare's father about her disappearance in Clare's room, when he notices a poster of an old woman giving the finger. Mrs. Mac looks at it, and then just nervously smiles.
- Hilarious in Hindsight: Bob Clark later went on to make A Christmas Story.
- Jerkass Woobie: Peter wasn't a nice guy by any means, but he certainly wasn't a killer. Too bad Jess didn't realize that. The scene where he phones Jess and begs her not to abort their child and starts sobbing is actually quite heart breaking and considering how everything else in his life is falling apart, you just kinda want to give the poor guy a hug.
- Nightmare Fuel: ALL OF IT!!! The numerous shots of Clare's corpse on the rocking chair in the attic, Barb's murder as a group of children carol outside, the phone calls...the ending!
- Paranoia Fuel: Any odd disturbances or noises you hear around the house? Somebody couldn't have broken in... could they?
- Retroactive Recognition: Billy is voiced by a young (and uncredited) Nick Mancuso, while Phyllis is played by a pre-SCTV Andrea Martin.
- "Seinfeld" Is Unfunny: It was, more or less, one of the first slashers.
- Signature Line: "The Calls Are Coming from Inside the House!"
- Signature Scene: Jess getting a glimpse of the killer's eye.
- Values Resonance: This article by Aja Romano views the film as having arguably more resonance in 2016 than it did in 1974. To wit: the killer, who harasses the girls over the phone before he comes to kill them, is basically a woman-hating internet troll before the internet. This harassment isn't taken seriously until it's too late, the film not-so-subtly blaming the community for allowing it to reach that point and fester within their midst (the famous line "the calls are coming from inside the house" can just as easily be seen as metaphorical). Finally, its portrayal of its sorority sister protagonists is quite sex-positive, especially by the standards of the time and the genre, including having the Final Girl not only be sexually active, but planning to get an abortion despite the wishes of her boyfriend.
YMMV / Black Christmas (1974)