u is for upside-down

I've said it before and I know I'll say it again: Dorothy's weird.  She likes to play with her toys upside-down!  Here are some photos of her doing it with Snoopy:

And here she is with the blue bone:

Sometimes she doesn't even need a toy - she'll just start rolling 'round upside- down on the floor for no reason, like a real crazy dog!  I always go over to her, hoping to snap her out of it, but she doesn't stop! She just tries to make me to do it as well.  As if!  I like my play time with all paws on the ground!  Does any one else know if this behavior is normal?  It's always confused me ... 

Bax