The Extreme Houdini is a sexual act with the following prerequisites: the couple must be having sex doggy-style, with the receiving partner facing a window on the first floor of the building. Another person, unbeknownst to the receiving partner, must be present in the room, usually hiding in a clost, as well.
The act is as follows: At a pre-decided interval, the giving partner pulls out and the hidden person must seamlessly take his place inside the orifice in question so as not to alert the receiving partner. Then, the original giving partner must leave the room, go outside and wave to the receiving partner through the window.
That ho was so surprised when she saw me waving after me and my friend did the Extreme Houdini on her.