“Since the perineum is so close to the prostate, pressing on it would be a way of getting in that general vicinity without doing anal stimulation,” Wiesner says. Or to put it another way, it’s a sort of back door to the prostate, without having to go through the actual back door.

Gay men who aren’t into anal sex tend to be well aware of this — grinding your taint against a partners’s knee while he jacks you off does a good job of stimulating the prostate, without the bother of sticking things into holes.

For that matter, some straight guys figure out that straddling the arm of a sofa (or some similar object) while masturbating can also enhance the orgasm, because your own body weight pressing against the perineum puts indirect pressure on the prostate.