Switcheroo

[Sarah]

when engaging in doggy style sex with someone in a [dark room], you breifly pull out, while a friend takes your place, with your partner [none the wiser]. while your friend is engaging in sex, you run around the house and wave at your partner [through the window].

[Dave Paprocki]

A change, reversal, or exchange, especially a surprising or deceptive one.

[Merna]

an unexpected change, especially one in which one thing or person is quickly or secretly exchanged for another: