Could a human feel the black body radiation of another human standing behind her? I've been thinking about infrared radiation and noticing more and more how the human skin seems actually pretty sensitive to it.
You can easily feel a bonfire from several meters away, far away from where any convection would heat your skin.
When you open the hood of your car you can feel the heat from the engine even standing back a step or two (away from the updraft of hot air).
Now try this: hold the palms of your hands against eachother a couple of inches apart and keep them like that for a couple of seconds. Then slowly (to avoid wind cooling) lift the other palm so they no longer face eachother. Do you feel it? For me there's a noticeable difference in warmth.
Is that the skin detecting black body radiation from other skin? This could be easily blind-tested with a friend; you hold your palm out and look the other way, then see if you can correctly tell when your friend's palm is near you palm and when its not. Maybe the human skin is even able to detect black body radiation from another human standing behind her? Kind of like a sixth sense. Could explain the sensation of "i knew someone was there".
I've noticed also that when you stand close to a concrete wall that was heated by the sun, but the sun has just set, you can tell which direction the wall is just from the heat on your body.
Is this all placebo or does it actually work that way?
 A: The simple answer to your question is "yes". The heat receptors on the surface of your skin can feel the infrared radiation, and there are enough of them on your body to make it a pretty good directional heat detector.
An aside, but related: I used to wonder in high school why I could feel this one girl staring at me from clear across the cafeteria. It was creepy at the time, and it still is - how you can feel someone in a crowd staring at you. I finally wrote a blog entry to try to explain the phenomenon. It's way too long. I have been told that it's simultaneously boring and entertaining, and I'm sure there are holes in the science. But it may give OP a better answer to his question. Here's the link: "I Can Feel Her Staring at Me!"
A: In principle, yes. In practice, it's going to depend on the sensitivity of the neurons involved. 
The reason it could be felt is because what you feel is not temperature but heat flow (or changes in temperature). At least, that's one way to explain the classic experiment where a person lets one hand sit in hot water for a while, the other in cold, and then moves both hands to a lukewarm water bath. The hand that was in hot will feel cold, and vice versa. When two people stand close together it slows down the rate at which both are losing heat, so it can be felt, in principle. In practice, it's going to depend on all sorts of factors: how cold is the air in the middle, is the wind blowing, how close are they, etc? 
Any experiment to measure this would need to be properly blinded with the person doing the sensing properly shielded from detecting the other person by other means (for example: hearing them, seeing their shadow, smelling them).
