Proof of cold fingers
I was at the First Lego League competition this weekend with my son. The biomedical school of Virginia Tech had some great research displays out. They had a very impressive high resolution infrared heat camera. This thing was so good it could show down to the eyelash level, which by the way don't conduct any heat.
My son and others were putting their hands and faces in front of it, and it showed a varying ranges of red for heat signatures. A cursor also allowed you to measure the temperature of any spot on the screen. I then put my hand up to the camera.
The operator and several other grad students working the displays all gasped. My fingers shown no red coloring whatsoever. My palm was red, but right about where my callousous are, the color went completely to grey/white and then by the very tip of the fingers, to dark grey. He took a temperature reading at my fingers and it came out at room temperature. No heat generation at all.
It was so freaky, but quantitatively and visually showed something that I've known for a long time. That I have cold fingers and toes.
The guy was saying that frostbitten fingers show up completely black on this camera. It's because the tissue and blood is actually frozen. People who try to rub their hands against each other to create heat from friction actually do cellular damage to frostbitten fingertips, because they are actually abrading the tissue away. Since it's frozen it's like chipping ice crystals away. It takes much longer to heal from frostbite.
This picture is nowhere near the resolution of the camera they had. Their camera was able to show the lines on the hand it was so good.