They look like they are having fun playing with it. It's a permanent sketch so they can just twist the knobs and shake it all they want.

*they twist the knobs and shake it like crazy*
Teehee! This is so much fun!
*Arthur clenches his fist*
I told you two to not touch my Etch-A-Sketch! Grrr!
*Cave Plushies laugh it off*
Heehee You call that a punch! XDD You hit like a girl.