A sexual act involving two men and one woman, done with the woman uninformed of the second man's presence. Doing the woman doggy style, the first man takes a second, tells his partner that he must "re-adust", and instead pulls his penis out, and quickly trades spots with the second man, while the woman is unaware of the change.
Best done in the dark, so as not to alert the woman of the presence of the second man, preferebly using a closet. Another method is done with the woman facing a window, in which the first man trades off, runs out side, and proceeds to wave at the now confused woman.
Rachel was shocked when Bob was doing her from behind, only to have him turn on the light switch from across the room. Meanwhile Eric laughed profusely, and had the living crap beaten out of him by a very angry Rachel. She did not like the Super Houdini they pulled on her.