Poop has stage fright often times, and by nature Poop is a very shy creature.  Often spending it's days it's dark places and small spaces, poop is by nature a hibernating type animal.  Consequently, before putting on it's grand show and final performance before it's ends it's life cycle by going to the porcelain throne in the sky, it will test the waters by releasing a formidably scented odor known as a "fart", "air biscuit", "hilary clinton", or "flatulence".  If all goes well and the fart is well received by it's environment, the elusive poop will come out of hiding.