"Capsaicin demonstrates the incredible elegance of evolution," says Tewksbury. The specialized chemical deters microbes—humans harness this ability when they use chilies to preserve food—but capsaicin doesn't deter birds from eating chili fruits and spreading seeds. "Once in a while, the complex, often conflicting demands that natural selection places on complex traits results in a truly elegant solution. This is one of those times."
Link -via Boing Boing
(image credit: Tomás Carlo)
Some of them like Blair's are really dangerous and when he makes them he wears a kind-of-hazmat suit!
And to know more about the Scoville unit :
http://en.wikipedia.org/wiki/Scoville_scale
By the way, that's how Icy Hot, tiger balm and other creams work to dull the pain: by overwhelming the pain sensors with heat.
ROFLLOL