Why do penises pulsate?

Penises pulsate due to a natural physiological process called vasodilation. When a man is sexually aroused, the arteries in his penis dilate or expand, allowing more blood to flow into the organ. This increased blood flow causes the penis to become erect and firm.

As the man continues to be aroused, the arteries that supply blood to the penis may constrict or narrow periodically, which reduces blood flow and causes the penis to momentarily decrease in size or pulsate. This process of vasodilation and vasoconstriction is what gives the penis its characteristic pulsating or throbbing sensation during sexual arousal.