When one
gentleman is anally
penetrating another, he stuffs both the penile shaft and testicles into the rectum. Following this, the 'giver' ejaculates, creating a "meaty filling".
Once the carnal act is completed, the 'giver' withdraws, but due to
the sticky concotion, the reciever's rectum prolapses, crating a sleeve around the filling, which closely resembles a scottish haggis.