When females shouted, males ejaculated 59 percent of the time. However, when females did not holler, males ejaculated less than 2 percent of the time.

To see if yelling resulted from how vigorous the sex was, the scientists counted the number of pelvic thrusts males gave and timed when they happened. They found when shouting occurred, thrusting increased. In other words, hollering led to more vigorous sex.