Why are chillies spicy?

Chillies contain capsycide which burns mammal taste buds, but buds can’t feel it. It’s the plants protection. It is not the seeds that make the chilies taste spicy but the white part around them does. It contains capsaicin and it does not "burn" anything but it does stimulate pain receptors found in the mucus membranes of the mouth. These receptors are called chemoreceptors and like the receptors for smells and taste (taste buds sense sweet, salty, bitter, sour and for some people tumami) are sensitive to chemicals in the environment. Plants have capsaicin to limit the kinds of animals that eat the fruit (peppers) or perhaps to cause them to spit the seeds out at a distance away from the plant thus dispersing the plant over further distances. Similar compounds are ginger (gingerol) black pepper (piperine) and surprisingly vanilla (vanilin), all have similar chemical structures.