Our dog (Murray) is caring and loving when it comes to humans, however around other animals it's a different story. He's very aggressive and will jump and bark uncontrollably when he sees other dogs. There was an incident about a year ago when he got out and attacked a neighbor's dog - neither animal ended up getting hurt however just a very scary situation. He's a rescue so we're not 100% sure of his history, however assuming there has been some trauma in his past. He's an australian cattle dog mix, and I would say he's in between mid-sized and small. Thank you!