Yoma 79 a, b

In discussing afflicting ourselves on Yom Kippur, the rabbis identify fasting as a form of affliction.  But might it be permitted to eat a very small amount of food and continue to be afflicted?  How much food might that be?

The rabbis focus on amounts of food that might be permitted on Yom Kippur.  Less than a date-bulk?  Less than an egg-bulk?  Less than an olive-bulk?  The rabbis debate about whether the date-bulk includes its pit or not.  Then they argue about whether a date-bulk might be larger than an egg-bulk.  What they want to avoid is eating enough to "settle the mind", which would lessen our affliction on Yom Kippur.

The laws of Sukkot and the laws of Pesach are used to untangle this debate.  On Sukkot, meals must be eaten in the sukkah.  Would a date-bulk count as a meal, or would it be a 'snack' that could be eaten outside of the sukkah?  The same questions apply to an egg-bulk.  And can fruits be called meals?  On Pesach, leaven is not permitted and leavened bread is not permitted.  But is a minimal amount allowed - and if so, how much?

The notion of measuring something important with an approximate measure - a date-bulk or a cubit - is remarkable.  Even more remarkable when we remember that the punishment for transgressing these halachot can be karet - death, excommunication, and/or death at the hand of heaven.  One would imagine that a very precise measure would be necessary to determine liability.  Perhaps there was more leniency in practice than it would seem.