The amount of blood on Maddie's white shirt goes from a lot in the safe room, to hardly any when they leave it, to a lot again when she goes back into the safe room.
Before Maddie goes into the trapdoor her pantyhose is ripped at the knees. When she comes up from the trapdoor her pantyhose is whole again.
In the car, driving to the party, Suzanne's "whiskers" change back and forth between shots.
When in the room with the symbols, Maddie begins to tell the story of what led to their present situation, and when she starts the story it is night time, but when she finishes the story, it is day time, yet she continues to tell the story and says that they will have to wait until dawn to escape the room, when it is clearly already day time.
After washing his face, Furlong's character somehow manages to get MORE blood on his face a few seconds later.