Your cock grows to a massive size, ripping your pants to shreds, your muscles grow, tearing you shirt open. Horns begin to grow out of your head, fur begins to grow over your body, two pairs of nipples form under the two you already had. Bit by bit, you slowly become an antrho bull.
Before you had the chance to wonder what just happened to you, a massive rush of lust envelopes you, and instinctively you begin to masterbate. Taking your cock in your hand you rub it up and down, slowly at first, and then faster and faster. Your pleasure increases more and more, you begin to buck you hips, thrusting into your hand.
Finally it was to much and you came a torrent of cum. Your mind clears enough to think 'I don't know what the hell just happened to me, but man was that intense. I think I'll stay like this.' While able to think you are still very horny and feel and urge to breed, and go in search of a partner.