Sleep barks!
I've seen Cooper do this only once. But what I really want to (& have been trying) to catch on camera is Max punching Cooper in the face. It usually occurs right after Cooper bites Max's mouth or after Cooper steals a toy that Max was just playing with. Max has a repeated one-armed punch right to the top of Cooper's head. I actually tried to capture it this morning but Max stopped as soon as he heard the camera turn on.