You’re a generous person (or not)
I make judgements about you based on your actions. University of Milan researchers had dogs watch some people sharing food with a beggar and other people telling the beggar to leave. Later, when the individuals beckoned the dogs at the same time, the pups overwhelmingly trotted over to the generous people.
You don’t like someone
When you have negative feelings about a person, I can hear your breathing pattern change, observe your body stiffen slightly, and even smell the subtle pheremones your body emits. So if your in-laws suspect that I don’t like them, it may simply be because, um, you don’t really like them.
Where you’ve been
You humans are like sponges. You pick up volatile organic compounds from everything you walk by or touch. If you just visited, say, the supermarket, I will smell the butcher and fish counters, the food you bought, and maybe even the people you stood next to at the checkout. I can smell something 100 million times more subtle than the faintest smell you can pick up.