Moed Katan, Chapter 1, Mishnah 8. This mishnah addresses the question of which kind of sewing is permitted on Chol HaMoed, and the law of stringing beds.
"HaHedyot tofer k'darko, v'ha'uman machliv":
The hedyot - a person who is not a tailor or a professional sewer - sews k'darko, in his usual manner. The uman, however, the professional tailor, is required to sew machliv.
Who is the hedyot? Several definitions are given:
One who is not skilled at passing the needle through the fabric several times so that a single pull produces many stitches at once.
One who is unable to produce a straight hem at the bottom of a garment.
Such a person may sew in his usual manner, since in any case his work will not come out professional.
What does "machliv" mean?
Some explain that he must skip every second stitch.
Others explain that the word derives from "kelev," a dog - the sewing is done like dog's teeth, up and down in a jagged pattern.
Either way, this is not professional work.
"U'mesargin es hamitos":
The mishnah moves to another activity: on Chol HaMoed one may string a bed. Ropes or straps were run across the width and the length of the bed, in both directions, forming the surface on which a person lies. This work was permitted on Chol HaMoed so that a person would have a bed to sleep on.
"Rabbi Yosi omer: af momsichin":
Some hold that the word "af" (also) should be deleted, since it is difficult to explain. "Momsichin" means only tightening the ropes that are already there, so that Rabbi Yosi's words are a stringency: one may not string the bed, but only stretch and tighten the existing ropes; there is no permission to put the ropes into the bed in the first place.
In summary: In this mishnah we learned that with sewing, the test is the status of the one sewing - the hedyot sews in his usual manner, while the uman sews machliv, whether by skipping every second stitch or by sewing in a jagged pattern like dog's teeth. We also learned that one may string beds for the sake of sleeping, and according to Rabbi Yosi - following the version that deletes the word "af" - only stretching and tightening the existing ropes is permitted, and not stringing the bed in the first place.