Chilies evolved a chemical that is interpreted as 'pain' by a select group -- mammals. Birds are largely insensitive to capsaicin (either orally, or ..uh, rectally.) See
here .
The best quote: "We eat chilies because it feels so good when we stop!"
- Pie
Tip: Never let your husband confuse teaspoons with tablespoons when measuring out the cayenne for the chili con carne.