Puppy Love?

I don't know what this means, whether it's a hint that he wants to play, a sign that he's finally in love with his little sister or if he's just keeping an eye on her. Everytime I enter the kitchen, Calvin is sitting, like a duck with his paws tucked under him, right by Phoebe's crate! When she's out, you'd think she was his arch nemesis by the way he growls, barks and avoids her. When I have to put her in her crate, he won't leave her side. I guess we'll just call it an odd case of Puppy Love!