Chullin 125

The mishnah at the top of today’s daf continues the discussion of how impurity is spread. In general, flesh is more prone to receiving and transmitting impurity than other parts of an animal — like bone, which is the focus of today’s mishnah:

With regard to the thigh bone of a human corpse and the thigh bone of a sacrificial animal that was rendered unfit as piggul, whether these thigh bones were sealed or whether they were perforated, one who touches them is ritually impure. The thigh bone of an unslaughtered carcass (neveilah) and the thigh bone of a creeping animal, one who touches them when they are sealed remains ritually pure. If one of these thigh bones was perforated at all, it imparts impurity via contact.

From where is it derived that even with regard to impurity transmitted via carrying there is a distinction between sealed and perforated thigh bones? It is derived from a verse, as the verse states: “One who touches the carcass thereof shall be impure until the evening; and one who carries the carcass thereof shall be impure until the evening” (Leviticus 11:39–40), indicating: That which enters the category of impurity via contact enters the category of impurity via carrying; that which does not enter the category of impurity via contact does not enter the category of impurity via carrying.

To understand this text, we need to clarify the relevance of a bone being sealed or perforated. In the Gemara, this distinction clarifies that our concern is with the marrow inside the bones. Marrow has the status of flesh, and therefore can receive and transmit impurity. In most cases, the bone itself is not a receptacle for or transmitter of impurity. A thigh bone — or, as many commentators note, any bone with marrow inside of it — can only transmit impurity if it is cracked and the marrow is exposed. 

However, there are two notable exceptions, according to this mishnah. The first is the thigh bone of a human corpse. A human corpse has a uniquely high ability to transmit impurity. For example, while most sources of impurity transmit when a minimum volume of an olive or an egg bulk is present, even human bones the size of a barley corn can transmit impurity — regardless of whether there’s any flesh or marrow present. This is a Torah-level law. The mishnah’s second case relates to a rabbinic decree. 

Like bones of a human corpse, bones of a sacrifice that is piggul also transmit impurity, even when sealed. (Recall that piggulrefers to a sacrifice that was offered with the intent to consume it after its permissible time and is thereby disqualified.) Though on a Torah level the sealed bones of a piggul offering should be pure, just like those of other animals, the rabbis decreed that the bones themselves could impart impurity to the hands. Presumably, this was to disincentivize priests from making sacrifices with wrong intentions. Therefore, in both the case of human bones and bones of a piggul, impurity can be imparted by the bone itself (and not just the marrow inside).

Let’s now consider the second part of the mishnah. After noting that for other animals the distinction between a sealed or perforated bone is significant, the mishnah goes on to prove that this distinction applies both to imparting impurity via touch and imparting it via carrying. There are some respects in which these methods of imparting impurity can differ. In this case, I might have assumed they do because whereas touching an unperforated bone means I haven’t interacted with its marrow at all, carrying a bone entails carrying the marrow within. So I might have thought even unperforated bones impart impurity via carrying. The mishnah assures us this isn’t true: Since the verse discussing impurity from a carcass juxtaposes impurity via touching to impurity via carrying, those two modes of transmitting impurity have equivalent rules with regard to the impurity of animal carcasses.

The impurity system, as one can see just from this single mishnah, is extremely complex. We cannot hope to master it in an essay or two, but these pockets of diving deep will, over time, help us appreciate the primary concerns and the ways the rabbis thought about the problem of tracking something that is so impactful yet largely invisible.

Read all of Chullin 125 on Sefaria.

This piece originally appeared in a My Jewish Learning Daf Yomi email newsletter sent on September 2, 2026. If you are interested in receiving the newsletter, sign up here.