Revealing mistake: When the guy standing on the right side of the fat woman is shooting on Simon Cowell you can't see any gunsmoke or fire coming out of the gun. (00:17:20)
Revealing mistake: As the one alien talks, look behind him. The seam where the two halves of the alien head prosthetic is visible on the second alien.
Revealing mistake: As the alien grabs George, the alien's finger bends backwards at an impossible angle, showing it's a glove. Also, the right eye of of the next alien is half way open, partially revealing the actor's eye.
Revealing mistake: When George comes flying out the window at Brenda's wake, if you look at his face, you can see it's a stunt double.
Answer: It was an alien in a Michael Jackson skin. He shed it and ran off into the bushes.
Grumpy Scot