He responds to emotion in pretty much any animal (or human) as far as I can tell. We also have an iguana (yeah, our house is a zoo...) and the iguana had to get

He responds to emotion in pretty much any animal (or human) as far as I can tell. We also have an iguana (yeah, our house is a zoo...) and the iguana had to get some eye medicine at one point. I was holding my son nearby when my wife was trying to catch the iguana (because at this point it had caught on to the whole medicine thing and it did not like it). This also elicited a cry from him, as if he even managed to sense fear or anger in the reptile. In that case, though, it's also possible he was just responding to the iguana thrashing his tail and trying to run away inside his enclosure. The sights or sounds may have just scared him that day or even the actions of my wife trying to catch the iguana, or something - it's hard to say for certain. As to why... I can't really ask him - he's not big on word use yet. :) I would guess, to some extent, that there's an instinctual desire to stay alive and that hostility can be a risk to that. Anger or fear could result in the people or animals around you doing something dangerous. It could also be a trust thing whereas anger represents a possibility that he can no longer trust your motives, maybe? I don't know - just guessing. :) It isn't just anger or fear that gets responses, of course. Happiness gets a big response, too, from a huge grin to joyful giggling to bouncing and other things that are like a direct visual indication of a burst of endorphins. I did just think of a dog parallel, though. When he cries out of fear when the dogs are playing too rough with each other or the cat, it's a bit like how dogs will correct one another in a pack. If you've ever observed dogs in groups greater than 1, they have this interesting dynamic where they will keep each other in line. One dog may get too excited and another will perhaps bark or nip at them to get them to settle down. Crying out of fear could be a similar response in the sense that it's all the baby can really do to inform the "pack" nearby that they need to calm down, please.