Kelim, Chapter Twenty, Mishnah Seven
A mat for lying upon was normally made in the following way: reeds would be placed across its breadth every four handbreadths. Lengthwise they would weave straw and other such material. People would lie between the reeds, because it was not comfortable to lie on the hard reeds. Our mishnah deals with mats made in an unusual manner.
1) A mat whose reeds stretched lengthwise is insusceptible to uncleanness;
a) But the sages rule: only if they lay in the shape of [the Greek letter] chi.
2) If they were laid along its width and there was a distance of less than four handbreadths between the two reeds, it is insusceptible to uncleanness.
3) If it was divided along its width, Rabbi Judah rules that is clean.
4) So also, where the end-knots are untied, it is clean.
5) If it was divided along its length but three end-knots remained intact across a stretch of six handbreadths, it is susceptible to uncleanness.
6) When does a mat become susceptible to uncleanness?
a) When its rough ends are trimmed, this being the completion of its manufacture.
Section one: According to the first opinion, since the reeds were laid lengthwise, the mat is not susceptible for impurity. A mat made in such a way must not have been meant for lying because it would be uncomfortable to lie on the reeds. But the other sages say that even though the reeds were placed lengthwise, one still could lie in between the reeds. It is insusceptible to impurity only if he places the reeds in the shape of the letter x (chi in Greek). Such a mat is certainly not good for lying because the reeds would be unavoidable.
Section two: If he didn’t leave four handbreadths between the reeds, then it is not good for lying and it is not susceptible to impurity.
Section three: If it was divided along its width, it is pure. Eventually the whole mat will fall apart because the straw will come undone.
Section four: The same is true if he unties the end knots. Since the mat will eventually fall apart, it is pure.
Section five: Ties are usually made every two handbreadths along the mat’s width. If the mat is divided along its length, but three end-knots remain on its width, covering a stretch of six handbreadths, that section of the mat is still usable and is still susceptible to impurity. Note that this is the minimum size in which a mat is susceptible to impurity (we will return to this subject in 27:3I bet you can’t wait).
Section six: Since we’re dealing with the purity of mats, the mishnah now answers the question as to when the manufacturing of a mat is complete such that it is susceptible to impurity. The answer is that it is susceptible once its rough ends have been trimmed. These are the ends of the tied knots.