Goofs

As the pizza girl walks along the street, she walks past the same pick-up truck three times.

When Maria is cleaning up the water on the floor the rag is red in one shot and then blue in the next.

Throughout the movie, the light in the foyer is always on, but through the window in the front door there's no light on.

The amount of blood on the killer's shirt after Janine's death changes.

In the shot before the killer cuts Diane with his drill, a bloody wound can be seen on her left hip. After the killer has officially cut her, she has the same wound on the same hip.

There's no contact information on the For Sale sign in front of Jackie's house.

When Duncan and Frank are murdered, their bodies are left on the floor of the foyer. In subsequent shots, the bodies have been removed and don't reappear until Jackie, Maria, and Diane head down to the basement.

When Ken stabs Diane to death, you can see that Ken is only stabbing the floor next to her.

Diane has a bloody wound on her left hip, before the killer actually cuts her with the drill.

When the killer uses chainsaw on his victim, it's obvious that there is no chain, which is made more obvious when he goes for the kill and there is no blood and chainsaw doesn't do anything.

As Janine reenters the living room, a woman in a white T-shirt and jeans can be seen in the room behind her.

After Sarah is killed, her friends are seen driving back home. A camera van is reflected on the side of the car, following it.