The amount of exfoliating mask on Frida's face changes from when she's sitting with the girls to when she runs to Jess' room to look for her.
Boa constrictors aren't venomous so they couldn't have made snake venom liquor from it.
Towards the end Slater is a talking to Frida and says everyone outside is dead. He's right but couldn't have known.
Right at the end of the film, the song playing ("The Boss" by The JB's) is not the one that is displayed as such on the screen.