Parah, Chapter 12, Mishnah 1. We now begin the final chapter of the tractate, and its opening mishnayos, the first three, all revolve around the same act: dipping the eizov into the mei chatas and sprinkling with it upon a person or an object that requires purification. Our mishnah opens with a problem of measurement.
"Eizov hakatzar": a short hyssop. The plant is simply not long enough. The water sits in the vessel, and when the eizov is lowered in, it cannot reach down far enough to touch the water at the bottom. What is to be done?
"Mesafko bechut uvekush": one may extend it, joining it to a thread or to a spindle reed, thereby lengthening the handle so that the hyssop itself can reach the water. "Vetovel uma'aleh": he dips it in this manner and lifts it out. "Ve'ocheiz ba'eizov umazeh": and then he takes hold of the eizov itself and sprinkles. The extension may serve for the dipping, but when it comes to the actual sprinkling he must grasp the plant itself. If he were to sprinkle while holding on to the attachment, that would be a problem.
"Rabbi Yehudah veRabbi Shimon omrim: keshem shehaza'ah ba'eizov, kach tevilah ba'eizov." Rabbi Yehudah and Rabbi Shimon object to the distinction. In their view, just as the sprinkling must be done while actually holding the hyssop, so too the dipping must be done while holding the hyssop, and not by means of an extension added on so that the plant can reach all the way into the mei chatas. Both acts are governed by one and the same rule.
Why should holding the eizov itself matter so much for the sprinkling? One explanation, given by Rashi, is a matter of aim. When your hand is on the plant, you control the sprinkling and can direct the drops precisely where they need to go. When your hand is on an attachment instead, the sprinkle may veer off to the side and miss its mark.
As for the halachah: although Rabbi Yehudah and Rabbi Shimon rule that an extension may be used neither for the dipping nor for the sprinkling, since the two must be treated alike, we do not decide the law according to them. We follow the first opinion of the Mishnah, which permits lengthening the short hyssop with a thread or a reed for the dipping, so long as the eizov itself is held in the hand when the sprinkling is performed.