Fun Factory Duke Prostate Massager - BlackDUKE THE PERFECT FIT. Two Toys in One. Did you know that your rectum (the fun few inches inside your butt) curves back toward your tailbone? That's why the DUKE is designed with a back facing curve: the bump at the top of the central shaft hits your prostate, while that curve gives you a feeling of fullness that's tailored to your anatomy. Oh yeah, and that extra section on the bottom? Vibrates your perineum, where there are lots of nerve endings.