What is the minimum that a person must eat in order to be held liable for consuming forbidden foods?
Generally speaking, Jewish law views “eating” as having consumed a minimum of a ke-zayit – an olive-size amount. Rav Yehuda quotes Rav as teaching that this principle remains in place for eating sheratzim – creepy-crawly things – which the Torah forbids to eat (see 11:42). In response to this teaching, the Gemara brings a teaching that was presented by Rabbi Yosei bar Rabbi Ḥanina before Rabbi Yoḥanan in which a passage in Sefer Vayikra (20:25) is understood as comparing eating such creatures with their status regarding ritual defilement. Just as ritual defilement exists when the creature is the size of an adasha– a lentil – similarly someone will be held liable for eating that amount.
What is the source of an adasha as a significant size in Jewish law?
The Gemara in Nazir (daf 52) quotes a baraita that compares two words in Sefer Vayikra (11:31, 32) – ba-hem, which seems to indicate coming into full contact with the animal will create a situation of tum’ah (ritual impurity), and me-hem, which seems to indicate that even coming into contact with part of the animal will create tum’ah. The baraita‘s suggestion is that even part of an animal will create tum’ah if its size is large enough to have been an entire creature. This minimal size is fairly small – ke-adasha – the size of a lentil – which the Gemara says is the size of a ḥomet when it is first born.
The ḥomet is one of the eight types of crawling creatures that are listed in the Torah as being tameh (see 11:30), but it is not clear to us what its proper identification is. Two different traditions have developed over the years in identifying it.