Fluttershy needed to go to the bathroom, but tried to hide it. She made the mistake of laying on her stomach, and ended up soiling herself, much to her embarrassment. At the same time, Sunset tried to fart, but ended up sharting instead and soiled her snow pants. So they had to stay in messy pants for a while before they could get home and change. And take a long shower. (Not that Pinkie and Rainbow don’t do it from time to time)
 
My first attempt at an onomatopoeia messing edit, by request. I’ll see how it’s received compared to my wetting and fart edits of this type.