The last section of a bowel movement that refuses to pass, instead coming to rest just inside the anus.
While not uncomfortable, the wiping process is greatly impacted. Unknown to the sitter their ass is clean, however, each wipe creates creates a slight relaxing of the sphincter which leads to light contact between paper and turd, making it appear that there is some mysterious and unexplainable trickery going on.
Jill: Who blocked the toilet with all this paper?
Ben: Sorry, I had a magic turtle.