Well...it has barbs on the inside that point towards the un open end, small barbs.
Idea being, that when Mr "Soon to be dead" rapist, slides his poor excuse for a tool, into his victim...he gets bitten...and when he pulls it out...its still there and HAS to be removed surgically.
Ergo, the hospital would then inform one of the Police Officers that are usually in Hospitals and he would be arrested under suspicion of being a vile and disgusting piece of sh*t and the victim, would obviously phone the police and give them a description so the two would marry up.
I assume, that it would be a snug fit, and also completely closed off at the far end, so...even if he doesn't go to the hospital straight away, he will have to at some point as piss gets pretty manky after a while.