Blow three whistles...

This is a real life incidence in my school here. One of my friend, a great cook of indian curries, packs is tiffin-box to school everyday. He shares the lunch time with his colleagues regularly and they all love the curries his prepares. One of his colleagues, an American, told him one day that she absolutely loves the 'chhole' he makes and would like to try the recipe herself if he could reveal the 'secret'. My friend, not able to communicate all the ingredients correctly in English, told her that he will email the recipe with most equivalent English condiment names. So he googled for enough time and prepared a long detailed recipe after a lot of pains:

"Get two tins of chick peas from grocery store. Empty them in a cooker and put water such that the water level is two digits of index fingure above the chick peas. Blow three whistles and let the chick peas cool down. Put some oil in a separate pot and deep-fry finely chopped onions and ......."

I am abstaining from putting the whole recipe here because I am lazy enough to type the whole thing but believe me, the document was in fact a very good beginners' guide to indian cuisines.

The lady read through the recipe, got all the condiments and ingredients from grocery store and started her experiment with the 'chhole'. In fact she was very satisfied with the results. Next day she told my friend about her adventure and the ultimate joy of success. She said, "The recipe was very detailed one and I hardly had any trouble following the things. But I don't understand one thing... Why do you have to blow three whistles?"

My friend tried to explain her that its a standard 'thumb rule' in India that by the time you blow three whistle the food in cooker should be cooked well, but the lady could not see any logic behind three whistles and well cooked food. She said, "Whats my blowing three whistles has to do with cooking of food in cooker? How is that food in cooker will be well cooked just by my blowing three whistles?"
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'Cooker' for the lady was 'electric rice cooker'. She never imagined 'pressure cooker' which is the most important part of an Indian kitchen.