Let's see..I think my boys understand more than they let on but:

Get Down
Come Here
No
Be Nice (when I can TELL they are about to scuffle!)
T-R-E-A-T-S (can hardly even SPELL it anymore without three kitty faces at my feet!)

Calvin knows "flipa flip" which is more of a trick..he then proceeds to flip over his head onto his back!

And when I say "WHAT"S THAT?" Calvin runs to the window to look for a squirrel or birdy

Claudia