Puppydog's Nose
When an individual is so ready to take a dump, the turd tip ever so slightly protrudes from the anus, usually about 1/8 to 1/4 inch, and in some cases, leaving a brown crayon drawing on the underwear.(also see shitstain).
While on the highway in morning gridlock, suddenly panic strickened, Marty felt the dreaded tickle of the puppydog's nose. At that moment, he knew any chance of a voluntary bowel movement was out the window.