Thai chilies at market.

They're what a lot of people think of first when the topic of Thai food comes up: Those teeny tiny innocuous looking chillies that don't seem like they could do much harm, but those that have carelessly eaten one on that assumption know better. David Thompson, in his compendium on Thai Food, refers to them as 'scuds' for their ability to sneak up on you and wreak complete destruction on your tongue.

The English name - mouse dropping chilies - of these tiny powerhouses is a direct translation of the highly descriptive, if rather rude, Thai name. Another English name is 'bird's eye chilies.' The chilies are used fresh in a number of dishes, where they are often ground to spread their flavor more evenly through the dish. While the chilies can be purchased in red or green colors, only the green ones are used in green curries, at least if you want them to be green.

Mouse dropping chilies

I often wonder what Thai food was like before the chili. The capsicum was only introduced to Asia from the new world about 300 years ago. You can credit Christopher Columbus' physician for the discovery of chillies, in 1493. Archaeological evidence from Peru dates the cultivation of the chili pepper back as early as 7000 B.C. It was the Portuguese who bought peppers to Siam and the rest of Asia. The Portuguese were the first westerners to make contact with Siam. The first envoy arrived in the Siamese capital city of Ayutthaya soon after the Portuguese captured the key port of Malacca in modern Malaysia in 1511, which at the time was nominally a vassal of Siam.

So, how did a non-native vegetable from the other side of the world come to play such an important role in Thai cuisine? There are a fair number of theories on this subject. One of the most common is the 'sweat' theory, which holds that since hot chillies make you perspire, they create an evaporative cooling effect. A more scientific sounding theory has it that the chili pepper's place in cooking is due to its preservative effect. In hot humid tropical climates like Thailand, food can spoil very fast. The oleo-resins that give the chili its heat also inhibit the growth of the micro-organisms that cause food to spoil. Supporters of this theory need to look no further for proof than one of Chiang Mai's most famous products: a fermented pork sausage called naem. Naem is made from raw pork, chopped mouse dropping chillies, a bit of garlic and not much else. The sausage is allowed to ferment for a few days to a week so that the chillies can do their work, but the meat is never cooked.

If you can't find mouse dropping chillies in your local green grocer, you can try substituting some other small chili, although the taste will not be quite the same. The Thai chili is most closely related to the Mexican Serrano chili. Both are technically strains of Capsicum annum, which surprisingly includes sweet bell peppers as well. The presence or absence of just one gene determines whether or not a pepper plant produces spicy or sweet fruits.