With a stipulation

The centaur laughs, looking both impressed with your gall and clearly unthreatened by your challenge. “Fine Cutie, you win in a game of riddles, you can ride on my back. But when I win, you’ll be my cock sleeve how I want, and I’ll take my time getting you to the city.”

You gulp at her sneer and shutter exactly what losing would entail, but agree. “Ok then, I’ll go first.” You think for a moment, and decide to go with a riddle you’ve long had memorized. “Here you go. What can run but never walks, has a mouth but never talks, has a bed but never sleeps, has a head but never weeps?“