I think my opinion on that is up in the air as I have yet to see a truely viscous dog in which the owner was not at fault. For instance, the infamous roommate pitbull is almost a year old but has never been aggressive to me as I have been around it now for awhile but will bark at neighborhood kids and neighbors. I think most of that is because it's been left alone for so long.

I do know that dogs when riled up, say been in a fight with another dog, will often bite the next hand that grabs it. That's just natural. It's not thinking its reacting.

In this case, the chessie is a natural protector. Anyone or anything that comes near a family member will automatically trigger the guarding effect. When it was at he vet, it wasn't use to that enviroment and was probably very uncomfortable. Get a very uncomfortable dog and a stranger approaching, you get a dog that will cower or bite.

Alot of these incidents are the most common that I've seen. The truely aggressive ones were made that way because of their owner. Truely aggressive, I mean, get loose and attack the first person, dog, etc. that they see.