The Torah in Parashat Metzora outlines the procedure that must be performed for a metzora to regain his status of purity. This procedure includes a ritual involving two birds, one of which is slaughtered, and the other dipped into the first bird’s blood and then sent away. The Torah requires taking for this procedure “shetei tziporim chayot” – “two live birds” (14:4), which Rashi explains as indicating that a tereifa – bird with a terminal illness – is disqualified for use for this ritual.
The question arises as to how the second bird’s status is to be determined in this regard. Some conditions that render an animal – or, in this case, a bird – a halakhic tereifa can be discerned only by way of an internal inspection after slaughtering. In the case of the birds used for the metzora’s purification ritual, only one of the two birds is slaughtered. The other is sent away, without ever be slaughtered. While the slaughtered bird can be inspected after its slaughtering to ensure that it had been suitable for this ritual, the live bird cannot. It must therefore be presumed suitable without any inspection. Apparently, this assumption is made on the basis of the general rule of rov, which allows us to rely on a statistical majority for halakhic purposes. Since most birds are not tereifot, we may presume that the bird taken for this ritual is likewise healthy, even though we are unable to perform a thorough inspection to verify this assumption.
However, if this is the case, then we must wonder why this halakha does not appear in the Gemara’s famous discussion in the first chapter of Masekhet Chulin (11) regarding the Biblical source of the halakhic concept of rov. The Gemara suggests several different possible sources, including a number of instances where the Torah disqualifies a tereifa for a certain procedure, despite there being no possibility of inspecting the animal. For example, in the case of an egla arufa – the calf that would be killed to atone for a murder when the culprit could not be identified – the Torah forbids dismembering the calf after it is killed, thus precluding the possibility of inspecting it to ensure it was not a tereifa. This is despite the fact that the Torah disqualifies the use of a tereifa for this ritual, thus establishing a Biblical source for the concept of rov. The Gemara also notes the example of the para aduma, the cow that would be slaughtered and then burned into ash, which was then used to produce the special water that was needed to purify people and utensils that had come in contact with a human corpse. The Torah requires burning the slaughtered cow whole, thus precluding the possibility of inspection, such that we must presume the cow to have been free of medical conditions that would render it a tereifa. This law, too, sets a Biblical precedent for the notion of rov. The question thus arises as to why the Gemara in this context does not also make mention of the live bird used for the metzora’s purification ritual. Seemingly, this requirement, too, reflects the halakhic principle of rov, and should thus have been invoked as a possible Biblical source for this concept.
This question was posed to Maharil Diskin, who offered several possible theories to explain why the live bird of the metzora’s purification ritual is not mentioned in the Gemara’s discussion of rov (Maharil Diskin al Ha-Torah). One answer he suggests is based on a possible parallel between the requirement to send away the live bird and the obligation of shilu’ach ha-kein – sending away the mother bird before taking her eggs or chicks. The Gemara in Masekhet Chulin (141b), as explained by Rashi (s.v. she-teitzei), establishes that once one sends away the mother bird, he may, if he so wishes, immediately capture it. The mitzva of shilu’ach ha-kein requires sending away the mother bird, but once this is done, one may then catch the bird immediately thereafter. This halakha is explicitly codified in the Shulchan Arukh (Y.D. 292:4). Maharil Diskin suggests that this halakha might likely apply as well to the metzora’s purification process. It stands to reason that, as in the case of shilu’ach ha-kein, the requirement is fulfilled the moment the live bird is set free, at which point it may be hunted if one so desires. As such, Maharil Diskin suggested, the Torah’s disqualification of a tereifa for this ritual does not necessarily prove the principle of rov. It is possible that the Torah expected the people involved to immediately capture the bird after it is set free to slaughter it and conduct an internal examination to ascertain that it was suitable for this ritual, and thereby confirm that the metzora has satisfactorily completed his purification process. Given this possibility – remote and far-fetched as it may seem – the requirement to use a healthy bird for this process does not necessarily prove that we may rely on the statistical majority, and for this reason, this requirement is not invoked as a possible Biblical source for the principle of rov.