Watched the making-of special the other day. Cameron (the director) sent a guy to the costume shop to pick out something creepy. He bought two, a typical "scary clown" one and the Shatner. Went back to the shop and pulled the eyebrows off the Shatner, mussed the hair, sprayed it white and enlarged the eye holes. When he showed Cameron the clown he said, "What else you got?" When he pulled out the Shatner everyone in the room got quiet and Cameron said, "Okay, that's him."