We have squirrels in our backyard and our dog loves to chase them (she never catches them). I believe she thinks they are giant rats with fluffy tails. They drive her nuts flicking their tails at her and then running up a tree. After she has "treed" one she just waits at the base not knowing that the squirrel has jumped to anther tree and is long gone by now. She knows that they go up the tree and then disappear... It's fun to say "squirrel" and see her take off.