It’s a button hole
As soon as I came home from work, I planted myself in the recliner and Karys came right over to crawl into my lap.
On the way up, her little hand stopped at my shirt pocket and she looked inquisitively at the button hole.
“What’s that?”, she asked.
“It’s the hole that the button goes through.”
“It’s what?”
“It’s a button hole.”
“Ohhh”, she said when the light bulb a-l-m-o-s-t clicked on. “It’s a butt hole?”

Oh dear, I’m still laughing. She is delightful and can come out with some of the funniest things!