 They must also be very smooth to avoid damaging the rectum or bowel.In order to get them into the rectum, they most commonly have a general profile of a round-ended cone which then narrows to a "waist" which locates itself at the anal sphincter, with the flared part outside the body, preventing the butt plug from slipping further into the body.The sphincter muscle will hold the plug in place by the waist, preventing the plug from slipping out unintentionally.