This is very simple people. Imagine a sauerbraten, but smelly and with the consistency of any of the following:
-Kit Kat bars
-a human finger
-etc (not too hard, not too soft)
Now picture this substance coming out of a homo-erectus' naughty spot (the bung cavity / choco-puddin' zone / rectum / sphinctrum-oreolis).
Finally, imagine this object smelling somewhat like a horse's baby-making-area. If one is unfamiliar with this scent, simply take a whiff after you go choco-potty (dropping the yong'uns off at le pool).
This, my friends, is Rectum Cake
Jordan: 'Mitchell, what's that smell?'
Jesse: 'Yeah it stinks'
Nolan: 'Mitchell tell me you didn't just-'
Mitchell: 'Yep, I made Rectum Cake! Dig in!'
Nolan: Why did you ruin my carpet ?!?!
Michael the Happy Squirrel left the presence of Mitchell due to the spliffage of his Rectum Cake.
To seep through fabric. Also to squeeze through very tight areas, such as pants and one's legs.
Jesse: "Dude you just made a doodie in your pantaloons"
Mitchell: "I know. It appears to be spliffing through the seams"
Michael the Happy Squirrel: "Dude get away from me. Your rectum-cake seems to be spliffing all over my fur"