@Linkat,
Yeah. Robert posted a video a year or so ago. Two teams dribbling a basket ball, and the audience was instructed to count how many times a particular team passed the ball - or something like that.
So, in the middle of it, they sent out a guy in a gorilla suit to kind of wander around among the players. Most of the audience didn't even see him. In fact, I had to replay the tape to be sure they hadn't added the gorilla guy later.
Pretty cool.