You walk down the hallway opening door after door and laughing at every joke you find in each one. As you walk to each door a tingle is growing in your rear at the top of your butt right where the butt cheeks meet. A first its only a red spot and hidden by your pants the small spot grows slowly bigger and bigger. After the 15th door you are still having so much fun you do not notice the soft bulge appearing there as the spot becomes skin color again.
You laugh at the jokes from the doors after each one as they get funnier and funnier.
"Ha ha ha ha ha ha ha!"
On the next three doors your laughing becomes strained for a short moment and more ragged. The soft bump is building more and more but being soft still is pulled flat by your pants as you walk.
"HA HAA HAW HAW HAW HAW HAW!"
Inside you your tail bone is tingling madly but you have yet to notice it. the ends normally turned inward are loosening slowly.