Did you know that the human body generates enough heat and energy to actually generate it's own light? That's right! But don't go turning the lights out yet, you already know you can't see it with the naked eye. That much should be obvious simply from observation. See, at the bottom of the Electromagnetic light spectrum is Red and just bellow that is Infrared... which puts it at just bellow the visible light spectrum for humans. But with technology we can see this light as was even utilized in the Predator movies. Just about all endothermic animals possess this light due to the fact that they generate internalized body heat. Pretty Awesome huh?!