That's so amazing! They groom eachother, that's adorable. It's kind of like cats I guess, they do that, too... well I think it's less social behaviour though and more ... uhm... one cat is trying to be more dominant over the other, maybe. But still, it's so cute when it happens, either way.
... I want a pet monkey, I think that would be so cute, but Angel would probably feel put out about the whole thing, actually. So I guess I'll have to live vicariously through you!
Oh, not that you have a pet monkey, because you already said that it was just a visit! But still, you're closer to having that experience than me, anyway.
They probably do get territorial about their food. It's one of many reasons why they're always saying not to feed the wild animals when you go out camping and to the parks and things. I always get so sad about that...