In the part where the Poltergeist comes back into the Freeling's house (towards the end of the movie), Diane runs into Carol Ann and her brother's room. The demon from the closet is sucking them in, and Diane grabs onto the door frame in order to keep from getting sucked in. Watch very closely at Diane's face when she tries to reach out her hand for Carol Ann. She has a moustache! Obviously, her stunt double is a man. It kinda freaked me out when I first noticed it...