Parah, Chapter 12, Mishnah 8. The final mishnayos of this chapter deal with the question of chibur, connection: when two parts of an object are regarded as a single unit, so that tumah traveling into one part reaches the other, and so that sprinkling the mei chatas on one part counts as having sprinkled on the whole. Our Mishnah opens, though, with a case of its own: a flagon of chatas water that became tamei from the outside.
The lagin of chatas water
The opening clause presents a "lagin", a flagon made to hold liquid, which is in use for the water of the chatas, and the tumah has come only upon its outer surface: "shenitme'u achorav". The ruling is "nitme'u tocho", the interior is drawn into that tumah as well. The Mishnah then extends the case: "umetamei es chaveiro vachaveiro es chaveiro afilu hein me'ah". This flagon passes the tumah along to a second, the second to a third, and the chain runs on even through a hundred vessels. In an ordinary case the tumah would come to a halt; here the exceptional standard of purity demanded for the chatas keeps it traveling from vessel to vessel.
A bell and its clapper
"Hazug veha'inbal, chibur." The bell and the clapper that hangs inside it are treated as one piece. The practical result is that if one sprinkles on part of it, the entire object becomes tahor, since the two are not two separate items but a single utensil.
The spindle of the reed worker
Next, "kush shel rovan": rovan is a species of reed from which mats are woven, and the kush is the spindle employed in that craft. Regarding it the Mishnah instructs "lo yazei", he should not direct the sprinkling "al hakush", onto the spindle, and likewise not "al hapika", onto the small ball fixed at its end. Neither of these is reckoned as the implement's essential body; the drops belong on the stalk. Even so, the Mishnah adds "ve'im hiza, huza": if he did sprinkle onto the spindle or onto the pika, the sprinkling is valid, since all of these pieces really are attached to one another.
"Shel pishtan, chibur." With the spindle used for flax, the parts are considered a connection from the outset, and the sprinkling is effective wherever it lands.
A cradle, a bed board, and handles
The Mishnah turns to a cradle: "ve'or shel arisah", the hide stretched over the cradle, "shehu mechubar lapikos", when it has been fastened onto the knobs of the frame, is "chibur", so that hide and frame are reckoned as one object. The board of the bed frame is another matter: "hamalben eino chibur", and the Mishnah spells out that this holds in both directions, "lo letumah velo letaharah". Tumah that reaches the one does not travel over to the other, and mei chatas sprinkled on the one leaves the other exactly as it was.
The closing clause: "kol yedos hakeilim", every handle of a utensil, "hadchukos", where a cavity was bored into the wood and the metal of the utensil was forced into it, carries the status of "chibur". Rabbi Yochanan ben Nuri would broaden the rule with the words "af hacharukos", including as well a handle into which the metal is merely wedged. We do not rule with him; the halachah stands with the first, anonymous opinion.
The thread running through the whole Mishnah is a single question asked again and again about ordinary household objects: is this one thing or two? On the answer depends both the path of tumah and the reach of the sprinkling that brings taharah.