Keilim, Chapter 15, Mishnah 6. Our mishnah gathers a series of rulings that share one common thread: in each case an object or a substance that would ordinarily be subject to tumah is declared tahor, either because it lacks the character of a keli (a receptacle), or because its use in the Beit Hamikdash removes it from the ordinary rules. The Mishnah opens with musical instruments.
The lute of the singer and the lute of the Levi
"Nivlei hashara temei'in": the lutes of the singers are subject to tumah. The nevel spoken of here is a small stringed instrument, shaped somewhat like the oud familiar from Arabic music, an oval body resembling a rounded guitar. In its face there is a round opening. That opening serves the sound of the instrument, but it served a second purpose as well: a musician playing for an audience and collecting from his listeners could drop the coins he received into it. Since the instrument therefore functions as a container, it can receive tumah like any other wooden vessel.
"Venivlei bnei Levi tehorin": the lutes of the Levi'im, the instruments played by the Levi'im during their service in the Beit Hamikdash, are tahor. These instruments also had an opening in their face, but no one ever collected coins in a Levi's nevel while he stood and sang at the avodah. For such an instrument the opening exists for one reason only, to enhance the sound. It is not a receptacle at all, and an object that is not a receptacle does not become tamei.
The seven liquids and the liquids of the slaughtering area
The Mishnah now turns to two halachot in which the law distinguishes between what belongs to ordinary people and what belongs to the Beit Hamikdash. The first concerns liquids.
There are seven liquids that carry halachic significance in the laws of tumah, remembered by the acronym yad shachat dam: water (mayim), wine (yayin), oil (shemen), honey (devash), milk (chalav), blood (dam) and dew (tal). Only these seven can themselves receive tumah, and only these seven can prepare food to receive tumah. Food, in the ordinary way, cannot become tamei at all until it has first been moistened by one of these liquids. That moistening is called a hechsher, a preparation of the food for tumah.
The mishnah first states the general rule, "Kol hamashkin temei'in": each of these liquids is itself capable of contracting tumah, and each has the power to prepare food so that tumah can afterward take hold of it. Then comes the exclusion: "Umashkeh beit matbechaya tehorin." The beit hamitbachayim was that part of the Azarah in which the animals designated as korbanot were slaughtered; there they were hung on hooks and skinned, their blood running out of them as they hung, and there the meat was washed down with water. Two of the seven are present in that place, blood and water, and in any other setting each of them would contract tumah and each would also serve as a hechsher. In that place they do neither. The blood of the korbanot and the rinsing water stay tahor, and the food lying about remains as unprepared for tumah as it was before. No verse teaches this; it is Halacha leMoshe miSinai, received by word of mouth from Moshe Rabbeinu at Sinai.
Scrolls of Tanach and the scroll of the Azarah
The second distinction of this kind involves Kitvei Hakodesh, the written scrolls of Tanach. Underlying the halachah is a practical concern of the Chachamim. A scroll is a sacred object and so is terumah, and it was only natural for a person to keep both in a single place. Terumah, however, is food, and food attracts mice, and once the mice came for the terumah they would chew through the scrolls and ruin them. Seeking a way to force the two apart, the Chachamim imposed a tumah: contact between a scroll and terumah disqualifies the terumah, and hands that have taken hold of a scroll pass that same tumah on to any terumah they handle afterward. Now that keeping the two side by side carried a real loss, people would store them separately.
Hence the rule of our mishnah: "Kol hasefarim metamei'in et hayadayim," every scroll of Tanach imparts tumah to the hands that hold it. Such hands take on the status of a sheni letumah, so that terumah they go on to touch becomes a shelishi and is thereby unfit. To this the mishnah adds a single exclusion, "chutz misefer ha'azarah," apart from the scroll of the Azarah.
That was the Sefer Torah kept in the Azarah, the Mikdash courtyard: from it the Kohen Gadol read on Yom Kippur, and from it the melech read at Hakhel, the mass assembly held on Sukkot in the year following Shemittah. Here the Chachamim saw nothing to be concerned about. Such was the reverence surrounding this one scroll that it would never have entered anyone's mind to leave his terumah lying next to it, and so there was no purpose in extending the decree to cover it. Hands that touch it remain tahor.
Further musical instruments
The Mishnah returns to instruments and to items of entertainment. "Hamarkof tahor": the markof is tahor. This was a toy horse fashioned by jesters for their performances. It contains no receptacle of any kind, and so it cannot receive tumah.
"Habatnun vehaniktemon veha'erus, harei eilu temei'in." The batnun is a stringed instrument that the player braces against his stomach. The niktemon was fashioned in the shape of the wooden leg worn by a man whose own leg had been amputated. The erus belongs to the percussion family: a thin animal hide is stretched taut across a hoop and struck by hand to sound it, along the lines of a tambourine. All three receive tumah, since the halachah regards them as receptacles. Several of them are hollowed out in front, and a musician playing before a crowd would drop the money he collected into that hollow. Because they functioned as containers, they are susceptible to tumah min haTorah.
To the erus Rabbi Yehudah attaches an additional category of tumah: "tamei moshav," it carries the tumah of an object meant to be sat upon. Were a zav to seat himself on it, it would turn into an av hatumah. His reason is "mipnei sheha'alaita yoshevet alav." At funerals there were women engaged to cry out and lament so that those standing by would be brought to tears, and such a woman would take her seat upon the erus while she wailed. An article that is put to use for sitting acquires the tumah of a seat.
Two animal traps
The mishnah ends with animal traps, each built from a wooden board rigged so that a plank drops and pins the animal. "Metzudat hachuldah temei'ah": the trap set for weasels does contract tumah, by force of a rabbinic enactment, since the way it is put together lends it the shape of a vessel. The one set for mice, by contrast, "veshel achbarim tehorah," stays tahor, being little more than a flat piece of wood with nothing of the character of a keli about it.
Across all its cases, this mishnah teaches one lesson from several directions. Tumah attaches to an object that holds something, and it attaches to substances that serve ordinary human use. A lute that never held a coin, blood that drained at the altar's side, a scroll no one would place his terumah beside, a flat plank laid out for a mouse: none of these is drawn into the world of tumah at all.