Animals are really sensitive to emotions and they tend to see people's true intentions better than any human could. It's a wonderful thing and that's one of the reasons we should credit animals more. I personally have seen it myself with the animals I've been with. When I was having some hard times with myself my hamster, even as a small pet, started to make noises in her cage so I could notice her and she'd jump on my hand and curl into a ball because she could sense something was wrong. My dog on the other hand likes to come lay next to me and headbutt my arm, like letting me know she's there for me.
It's a wonderful thing, I need to admit - and it's not just only related to sad emotions. To all types of ones. I'm really fascinated about this whole thing, I gotta say!