One of my BO's knocks 3x on our sliding glass doors when she wants a treat. Or is bored. Or maybe she just likes her reflection.
She's also the one that sits at the picnic table with my children in the summertime. We've put a plate of food on the table in front of her, just to see if she would lose her manners she would jump up on it. But no. She sits politely on the bench and eats like the other nice kids.