Plug-n-play?
If the proverbial Martian anthropologist tried to form his impression of humans solely by watching our "local" "news" broadcasts, he'd conclude that humans come in two forms. These two forms appear to be the upper and lower parts of one complete creature. He'd theorize that the upper and lower parts sometimes get glued or clipped together, but the resulting complete creature is never seen on TV. Perhaps it becomes invisible, or perhaps it travels to private areas to spawn or die.