Penis captivus occurs when a man is unable to withdraw his penis from a woman’s vagina.

During intercourse, a man’s penis is filled with blood and remains so until he ejaculates. When a woman has an orgasm, her pelvic floor muscles contract rhythmically. When these events occur at the same time, it’s possible for the penis to become “stuck” in the vagina for several seconds.

Eventually, the woman’s contractions stop and blood leaves the man’s penis. No longer erect, the man is able to withdraw and the couple can separate.

Penis captivus is extremely rare in humans.