This prisoner has the perfect escape plan

Carl is in the 10th year of a life sentence when he gets a new cellmate, Jim.

… after taking some time to size Jim up and decide that he can trust him, Carl tells Jim about his plan to escape.

“You see,” Carl says, “For the first 5 years I was inside, I trained my digestive system to follow my command.  Now I can eat something and it comes out broken down into it’s components.”

Jim is sceptical, but intrigued.

Carl continues, “For the last five years, I’ve been swallowing pieces off my uniform.  It’s perfect, because the guards just think it’s rats chewing on it.”

So Jim asks, “Well, what does that have to do with me? How can I help?”

Carl says, “Well, the pieces of fabric come out as individual fibres.  I figure by this time next year, we’ll have enough to fashion enough rope to get over the wall.  I just need you to tie the fibres.”

Jim, disgusted, says, “You have got to be kidding me!?”

And Carl says,

“I shit. You knot.”