“But here's the strange part: VR1 receptors weren't designed to detect capsaicin. They bind spicy food by accident. The real purpose of VR1 receptors is the detection of heat. They are supposed to prevent us from consuming food that is too hot, in the thermal sense. (That's why our VR1 receptors are clustered in our tongue, mouth and skin.) So when they are activated by capsaicin the sensation we experience is that of excessive heat. We start to sweat and get the urge to drink lots of water. But that pain is just an illusory side-effect of our cell receptors. There is nothing "hot" about spicy food.”
So hot is hot because our senses mistake spice for heat and react to save us from ourselves.
Brian freeze is caused because the roof of the mouth gets cold which lowers the temperature of the brain, the brain interprets the temperature drop as death, the brain sends out signals which then causes the heart to pump all available blood to the brain, which causes brain freeze. That is the hot, spicy and cold of it.
