Plot hole: If Marybeth was able to seal her nostrils and use her extended finger to remove the cap and make nobody suspicious about her, why didn't Delilah do the same thing? She was alien, so she should've still been able to do it, same as Marybeth.
Factual error: Zeke is in his car trying to fight off Miss Burke and they crash into the school bus, causing an explosion. The gas tank in Zeke's car is under the trunk of his car and the gas tank to the bus is in the rear of it. Everything underneath both hoods is mechanical and nothing is combustible at the front where the impact occurs.
Continuity mistake: When you first see Delilah at the start she puts her hair behind her ears. When the camera angle changes her hair is in front of her ear again.
Continuity mistake: Towards the end of the film, the students gather around the fish tank in the classroom. In the close-up scene the tank is brim full (the students actually touch the water when they lean on the tank). However, in the long shot, the tank is only half full.
Visible crew/equipment: In the scene where Coach Willis tells Casey he did some fast running and there is plenty of chasing on the field then the camera cuts to showing Casey and his father, the tip of a boom mic is visible at the top of the screen. (00:34:00)