I have been thinking about this towel test for judging the smartness of your dog and I wonder if the towel size is a factor. A bath towel over Ricky would be like a blanket over a lab. Wouldn't seem like a fair test.
Also, chihuahua are more likely to bite because most small dogs are protected from strangers by their owners. I know Ricky had that incident but most people, even the person he "bit" can pick him up etc. So I think it is more like the owners of certain breeds tend to act in some way that makes the behavior the way it is. I may be way off on that though.