When a dog sits and pulls itself around with its front legs in an effort to scratch an itchy butt hole. It's an act that is often unexpected and hilarious (if it's not on your rug.)
Nancy - "Do you like our new carpet?"
Thomas - "You're so brave to install white carp-HAHA, Muffin is totally scooting by the chair!"
Nancy - "MUFFIN! NOO!"