Revealing mistake: A quick mistake happens when Brenda and the girl crawling out of the TV get in a fight. Brenda throws the punch, the other girl falls over, and for a quick second her dress flies up too far and you can see where the makeup (that makes her look dead) on her legs end and you can see her real thigh.
Continuity mistake: After George has closed the well, the alien appears. Cody and Cindy gasp, and you see Cindy putting her arm on Cody's right shoulder. George climbs up from the hole and puts his hand on Cindy's shoulder. When it cuts, Cindy's hand is on Cody's left shoulder and George's hand is on Cody's right shoulder.
Continuity mistake: When Cindy is surfing the Internet for the lighthouse, you see her clicking on different links. When she has clicked the "Page4" link, you see the mouse pointer start moving. Then it cuts to Cindy and back to the screen again. You can see the mouse pointer move from the exact same position in the exact same direction.
Revealing mistake: When Tom comes down to the basement you see him coming down a narrow stairway. Later when Cindy says "there's something on the other side of the door", you can see a shadow walking back and forth behind the door. That shouldn't be possible unless the thing behind the door can walk through the walls in the narrow stairway.
Continuity mistake: When Father Muldoon is knocking on Cindy's door, she walks towards it. It is a frosted glass door, but you should be able to see if someone is standing behind it. We can't see Muldoon standing there at all. It cuts to Cindy opening the door, and then back to Muldoon standing in the door opening. We can also see a painting in the hall, and when Cindy closes the door we can see the painting through the glass door. How come we didn't see Muldoon?
Continuity mistake: When Tom is talking to George at the farm about his hip-hop dreams, on his right hand he is wearing a glove and is also holding another glove. The glove stays on all during the conversation, and we never see him take it off. Then, when George gets his head stuck in the bus, you can clearly see both of Tom's hands - empty.