What is up the cheerleaders' skirts?

Based on the ghastly reactions of the cheerleaders holding up their fellow cheerleaders, there must be something pretty horrible going on under their cheerleader skirts. My mind is racing around the possibilities (like maybe they both simultaneously soiled themselves from a night of eating copious amounts of Taco Bell) but take a guess. I'd love to hear the range of possibilities.

What lies beneath the skirts of these cheerleaders to draw such shocked reactions?