The fruit of "most" species of "Capsicum" contains capsaicin. Capsaicin is a chemical that can produce a strong burning sensation in the mouth (and, if not properly digested, anus) of the unaccustomed eater. Most mammals find this unpleasant; however, birds are unaffected. The plants developed the secretion of capsaicin to protect the fruit from being eaten by mammals. At the same time, the bright colors attract birds. These birds will spread the seeds. The amount of capsaicin in peppers is highly variable and dependent on genetics. This means that almost all types of peppers have varied amounts of heat felt by those consuming them. The only pepper without capsaicin is the bell pepper. Chili peppers are of great importance in Native American medicine. Capsaicin is also used in modern Western medicine to stimulate blood circulation or to relieve pain.