Ditto the responses on dogs smiling; they don't smile. That's an example of humans projecting their behaviors onto animals.

Ditto too the responses about interpreting dogs' behaviors. With repeated interactions, I develop knowledge of whether a particular dog is benign or vicious; on a first meeting, though, I wouldn't bet my physical well-being on my interpretation of a dog's intentions.

I ride a lot in Amish country, and some of them let their dogs roam free...And they generally don't vaccinate their dogs. Hence, a random dog bite could entail significant risks. If I can't outsprint a questionable dog, I just avoid it altogether.