My grandma had one for years. Good dog, no behavioral issues or aggression. Very loyal. He did have a big fear of storms, but that's not necessarily a breed issue. Kind of reminds me of a chihuahua, but didn't have the fearful aggression that a chihuahua sometimes has. Didn't run off when outside. Someone mentioned a jack russell, but I don't think a rat is anything like that, at least this one wasn't.