Inside/YMMV

Alternate Character Interpretation: A few for La Femme. Many feel that La Femme (including her actress Beatrice Dalle) is misunderstood given what happened to her and that she isn't necessarily "evil". Another theory floating around (due to Sarah's comment about there being no survivors) is that she died in the car accident and is a ghost haunting Sarah.
Non Sequitur Scene: Sarah has a dream where she starts vomiting, followed by her baby bursting out of her mouth.
Evil Is Sexy: There's probably quite a few people who answered "Me!" to Sarah's rhetorical "What kind of man would fuck a maniac like you?"
Faux Symbolism: The house number being 666, coupled with the Christmas setting and the seemingly teased Maybe Magic, Maybe Mundane.
Foe Yay: In one scene, Le Femme gets unsettlingly intimate with Sarah.
- Later on, when Sarah is about to give birth, La Femme comforts her and tells her that she's right here...while cutting open her stomach with a pair of scissors.
Nausea Fuel: So much gore.
Nightmare Fuel
Paranoia Fuel: Watching this while pregnant is ill-advised.
Special Effects Failure: The in-utero baby, and a brief shot of the Aerosol Flamethrower.
Squick: The very concept.
The Woobie: Sarah.
Woobie, Destroyer of Worlds: La Femme was driven insane by the loss of her unborn child.