Etiquette, as a matter of fact, is central to most traditions of hand-to-mouth eating; the artfulness and ritual of the practice is part of what people love about it. Hand-washing often comes first. In Muslim communities, a prayer of thanks comes next. Only then can one reach in — usually with just the right hand — to eat.

And dining with the hands is not necessarily easy: in some regions, including parts of India, it is most polite to use your thumb, pointer and middle finger, and to let only the first two joints of those fingers touch the food.

Details differ from place to place, but often rice or flatbread is used to ferry food to the mouth — think of Indian roti and naan, Ethiopian injera or Middle Eastern pita. Central and Southern Africans pound root vegetables or corn into starchy mashes like fufu or ugali; you’re meant to pull off a bite-size ball and use it as an edible scoop.

Ms. Sahni refuses to eat Indian food with a knife and fork, even in the most formal South Asian restaurants in New York. “I don’t care if I’m all dressed up, if everyone else is eating with a knife and fork, if the wine pairing is $80,” she said. “It’s essential.”