I think many Cavaliers still have a hunting instinct. Tess certainly does. If I say "squirrel" and open the back door, she's out of the house like a shot. And she was frantic when we brought home parakeets years ago... Could not understand why "those things" were inside the house and she couldn't have them. LOL And when we got a mouse, she knew long before we saw any droppings... and she helped us get rid of it too. My two Goldens on the other hand, are only moderately interested in squirrels... it's Tess who sees them and starts barking up a storm.