grow a tail

Etymology
To grow a tail is a metaphor, as the anus where poop exits is adjacent to where a tail is placed. "Growing" in this case refers to partial expulsion as one attempts to prevent it.

Verb

 * 1)  to be nearly about to defecate, to the point of being unable to completely hold it in
 * 2) * 2000 Larry Glanz The Ultimate Book of Bathroom Etiquette and Humor pg 146 and pg 152
 * When man needs to grow a tail, man must run to bathroom without fail. Thou shalt groweth thy tail with great care, or though might staineth thine underwear!