Reference for Keritot 41:46

דכוותה גבי בהמה לאחר מיתה אי בשר מטמא טומאה חמורה ואם דם מטמא טומאה חמורה דתנן

implies: as seed is characterised in that it will at no time convey weighty uncleanness and requires preparation, so everything that will at no time convey weighty uncleanness requires preparation! - He replied: This holds good in cases where the edibles have not joined to them less than an olive's bulk of nebelah; in our instance, however, the food has joined to it less than an olive's bulk of nebelah, and since it would require no preparation if it [the nebelah] was made up to a full olive's bulk, [so it requires no preparation even now].

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