I too was thinking he seemed big for a Chihuahua! He's a little mystery pup. As for his behavior, he is very trusting, doesn't mind being picked up and held. He sleeps a lot during the day, and then has a little bit of a crazy hour at night with lots of biting (we're working on this but he's still so young). He is not very aggressive on walks, more of a sniffer and a meanderer, sometimes just stops until he's picked up. But mostly I am impressed with how smart he is. He already knows "sit" and our friend trained him to "lay down" in under an hour. Also he came to us nameless at ten weeks old, and learned our name for him (Otto) in three days. So far that's all I know about this little guy, thanks so much for the help!