Storm knows the word treat so well that now I have to spell it out. I sometimes think that he also understands this. He also knows the words: no, down, birds, bedtime, and his name. He also has selective hearing.

Sunny knows the words: no, down, and he knows his name. He also has selective hearing. He knows the word treat only because he sees Storm responding to it.

Cirrus doesn't know his name yet and I'm not sure what else he knows but I think he'll learn in time.