Dogs pick up on things we don't; the question is how often those things mean what the dog thinks they do. When I was a teenager, we had a dog. My parents had one friend who the dog would not settle down around. Our best guess is that the dog somehow smelled the medication the man was taking for epilepsy. Or it may have been random: what I know is that this man spent years visiting us semi-regularly, and as far as I know never stole anything or harmed anyone in the household.

I'm not saying "don't trust your dog in this sort of situation," because part of the point of things like The Gift of Fear is that there are times when it's worth risking a false positive. Not trusting those random strangers did boxofdelights no harm, and ignoring her dog might have been unwise. (If one of them had been bitten, and she had been shoved to the ground, everyone would have been worse off, possibly including the dog.)