It turns out that capsaicin – the active ingredient in spicy food – binds to a special class of vanilloid receptor inside our mouth called VR1 receptors. After capsaicin binds to these receptors, the sensory neuron is depolarized, and it sends along a signal indicating the presence of spicy stimuli. 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 thermoreception, or the detection of heat. This means that they are supposed to prevent us from consuming food that will burn our sensitive flesh. (That’s why our VR1 receptors are clustered in our tongue, mouth and skin.) As a result, when the receptors are activated by capsaicin, the sensation we experience is indelibly linked to the perception of temperature, to the feeling of eating something near the boiling point of water. But that pain is just an illusory side-effect of our confused neural receptors. There is nothing “hot” about spicy food. The larger point, of course, is that vast swaths of the reality we take for granted are mere accidents of anatomy.