One of the places that really sticks out for me is if your local mall has a kids play area with the little toys they can climb on. You see all the parents lounging, checking each other out, around the perimeter, not really speaking, just watching the kids. The kids playing in the most raw and instinctual way. Lol.
Another time I see it a lot is when I happen to notice and observe a man and women flirting with each other.
I think you are right that it is in the body language. The subtle cues where one lets go of their form and starts acting from an unaffected base instinct.
For example the way a woman cocks her hip to the side, softens her voice, turns her head slightly, smiles more, and wiggles a bit when speaking to a man she finds attractive. Then the way the man responds by standing up a bit straighter, cocking his elbows slightly outward, and puffing up his chest. They way they look at each other nervously as though sniffing each other out. I don't think most people notice those things, but when you tune into the movement of them, it looks very, primal. People start appearing very simple.
Edit: I am going to look into this Paul Ekman. Sounds like a good read.
