Chauvihar is the vow to take nothing at all — no food, no water, no medicine — between sunset and sunrise. A lighter form, tivihar, permits water. Monastics keep it absolutely. The reasons given are consistent across the literature and are about himsa rather than health: lamps and fires attract insects into cooking pots and onto food; darkness prevents you from seeing what is in the bowl; and digestion, in the traditional physiology, generates more subtle life when food sits overnight. The rule was formulated when the alternative to daylight was an open flame, and observant Jains keep it under fluorescent light in Mumbai and New Jersey, which tells you the rule is now doing something other than what its rationale describes — a form of daily discipline whose original justification has been overtaken and which is maintained anyway. It is socially demanding in ways that are easy to underestimate: it rules out dinner meetings, evening restaurants and most of adult professional life after six, which observant Jains simply arrange around.