When Derric meets Becca in the school corridor and opens his backpack, it doesn't close completely when he puts it on his back; it's closed in the next scene.
When Becca tries to seduce Edward, a circular light hanging from the ceiling in the background is switched on. When Edward throws Becca through the ceiling, the light is still on. When Becca falls through the ceiling, the light is off.
When Alice is climbing out of the hole, someone throws a cell phone in her face. The phone-thrower's hand appears briefly on the right side of the screen.