Describing something hard to describe

We're playing Lincoln Logs on the floor, we're casually talking about school. Magoo stands to tell me how to carry the rods. He suddenly has a new expression on his face, something has just occurred to him.

"I need to have a bowel movement."
He turns away.
Takes two steps.
Turns back.
Hands move up toward cheeks then up and away.
"See, when I need to have a bowel movement, I get all sparkly."