Boo has a profound sense of empathy towards all living things, save for the ones who try to hurt others that he cares for. He and Tucker share an extrodinarily strong bond, equally shared by the rest of Tucker's family. Both Tucker and Boo consider themselves to be "brothers", which is why Tucker sometimes refers to Boo as "brother" often.
Boo is like any other dog. He has the ability to scratch, bark, bite, etc..