When Willow was a puppy, she liked to guard her extra treats waiting to see if someone would try to take them; or go running around like mad tossing them around playfully until finally eating them at her leisure.
When Corky was a puppy: she tormented him much like he is doing now. Sitting there, guarding the her treat while he sat there wanting to eat it. Thus when moments like this happen: I think of it as a Corky's revenge. Willow taught Corky well, too well, in fact.
Coincidentally: Misty is the one who tends to sneak in and nab the threat, if Corky leaves instead of eats it, lol.