== Penile erection ==
In males, sexual arousal typically shows in a penile erection, which is a swelling, hardening and enlargement of the penis. Such an erection enables [[sexual intercourse]] and is also usually present during [[masturbation]]. After [[ejaculation]], the erection usually ends.
A non-sexual cause of penile erections is REM sleep. The phenomenon is colloquially known as ''morning wood'' (AE) or ''morning glory'' (BE) when present when a man wakes up.