small fuzzy creature (often slimy) who spawns from one's anal reigon. these "ass grebils" are often the cause of prolonged constipation. however these rectal-rodents can be excreted and usually are.
*how to know that YOUR ass gerbil has been ejected*
1) your feces has sharp claw-like points that scrap your cheeks
2) your feces is steaming in the toilet
3) your feces is completely impossible to break-up or compress
boy1:"wow! my very first ass gerbil!"
boy2:"cool! what color is yours?"
boy1:"orange and red!"
boy2:"wow! mine is green!"