Nazir, Chapter 5, Mishnah 7. Like the two preceding mishnayos, this mishnah also deals with a case in which a person accepts upon himself a vow of nezirus that depends on a question of fact.
The koy - a doubtful case: wild animal or domesticated animal:
The mishnah opens: "Ra'ah es hakoy" - a person sees an animal called a koy. The status of the koy in halachah was in doubt, whether it is judged as a chayah (a wild animal) or as a behemah (a domesticated animal): a chayah is an animal that is not domesticated, and a behemah is an animal that is domesticated. There are halachic differences between the two in several areas:
Covering the blood: when a behemah is slaughtered, there is no need to cover its blood; when a chayah is slaughtered, there is an obligation to cover its blood. A deer, for example, is a chayah, and a cow is a behemah.
Cheilev: certain fats of a behemah are forbidden to be eaten, while those same fats in a chayah are permitted.
The case in the mishnah:
The mishnah describes a group of people who were traveling on the road and saw a koy, and each one of them accepted upon himself nezirus dependent on the definition of that animal:
"Hareini nazir shezeh chayah" - on condition that the koy is a chayah, an animal that is not domesticated.
"Hareini nazir she'ein zeh chayah" - on condition that it is not a chayah.
"Hareini nazir shezeh behemah" - on condition that it is a behemah.
"Hareini nazir she'ein zeh behemah" - on condition that it is not a behemah.
"Hareini nazir shezeh chayah u'behemah" - on condition that it is both a chayah and a behemah.
"Hareini nazir she'ein zeh lo chayah v'lo behemah" - on condition that it is neither a chayah nor a behemah.
All of these definitions are correct: in certain respects the koy is considered a behemah, in certain respects a chayah, in certain respects both, and in certain respects neither one nor the other.
To this the mishnah adds three further acceptances of nezirus, which depend on the nezirus of those who spoke before them:
"Hareini nazir she'echad mikem nazir" - on condition that one of them is considered a nazir.
"Hareini nazir she'ein echad mikem nazir" - on condition that none of the people listed above is considered a nazir.
"Hareini nazir shekulchem nezirim" - on condition that all the people listed above are nezirim.
"Harei kulam nezirim":
The conclusion of the mishnah is that they are all considered nezirim. According to Beis Shammai they are all nezirim with certainty, since in their view nezirus accepted in error is nezirus: even if the person was mistaken, and even if the condition he stipulated is not correct, he is a nazir. According to Beis Hillel, as we learned in the view of Rabbi Shimon, he is a nazir out of doubt - there is no ruling as to whether he is a nazir or not. Therefore he must observe nezirus conditionally, and state on the side: if in fact I am a nazir, let me be a nazir; and if not, then I am a nazir as a voluntary undertaking.
In summary: in this mishnah we learned about nezirus that depends on the definition of the koy, whose status is in doubt between chayah and behemah (regarding covering the blood and the prohibition of cheilev), and about the series of conditions stipulated by those traveling on the road - concerning the koy itself and concerning the nezirus of their companions. The mishnah rules that "they are all nezirim": according to Beis Shammai with certainty, because nezirus accepted in error is nezirus, and according to Beis Hillel out of doubt, and therefore he should observe nezirus conditionally and as a voluntary undertaking.