Penis captivus may sound like some sort of made-up X-rated wizard spell, but it is actually the name for an existing occurrence. Penis captivus is when a man’s penis gets physically stuck in a woman’s vagina. The cause is unknown, but it is suspected that it has to do with a woman’s vaginal muscles contracting during orgasm. This is rare and generally only happens for a matter of seconds, but it’s still enough to scare some away from sex for a while.