Machshirin, Chapter 1, Mishnah 6. Throughout this tractate we are measuring whether water reached food in a manner that pleases its owner. Only such water, called "b'chi yutan," makes produce machshir l'kabel tumah. Our mishnah collects several cases in which liquid certainly arrived on the food, yet we must ask whether the owner had any interest in its arriving there at all.
"Hanofei'ach ba'adashim l'vodkam im yafos hein," one who blows on lentils in order to test whether they are of good quality. This was the accepted method of examining lentils: a person would blow on them, and by how much dirt and refuse flew off he would judge whether the batch was worth buying. Where does liquid enter the picture? The Rav explains that as a person blows, droplets of saliva leave his mouth and land on the lentils, and saliva is one of the liquids capable of giving food hechsher l'kabel tumah.
"Rav Shimon omer: einan b'chi yutan." Rav Shimon holds that this saliva is not b'chi yutan. The man's purpose was to blow away dirt, not to wet his lentils with spittle; the droplets were never wanted, so they leave the lentils untouched by hechsher. "V'chachamim omrim: b'chi yutan." The Chachamim disagree. Anyone who blows knows perfectly well that saliva will accompany his breath. Since the result was entirely predictable, it is treated as though he intended it from the outset, and the lentils are machshir l'kabel tumah.
Next the mishnah turns to "v'ha'ocheil shumshemin b'etzba'o," a person who eats sesame seeds by means of his finger. Sesame seeds are tiny, and the practical way to eat them was to put a finger into one's mouth until it was coated with spittle and then press it down onto the seeds; they cling to the damp finger and are lifted to the mouth that way. Only a single finger does the work, yet as the eating continues the wetness gradually spreads across the entire hand. The mishnah's question concerns exactly that moisture which ended up elsewhere on the hand: does it qualify as b'chi yutan?
Rav Shimon rules that it does not. What this eater wanted was a damp fingertip, since that was his tool; moisture spreading over the rest of his palm served him in no way whatsoever. Liquid that a person places no value upon is not b'chi yutan and cannot bring food to hechsher l'kabel tumah. "V'chachamim omrim: b'chi yutan." The Chachamim hold the opposite, resting on the rule taught at the head of the perek, the principle of "techilaso b'ratzon": once the wetting began with a person's consent, the liquid counts even where its continuation was never something he desired. The moistening here started by his own will, so everything that followed is drawn along with it. Rav Shimon by no means rejects that rule. His argument is that with regard to the hand there was no willing beginning to speak of, because the man's entire intention was directed toward his one finger and extended no further.
"Hatomein peirosav bamayim mipnei haganavim, einan b'chi yutan." One who hides his produce in water out of fear of thieves has not given it hechsher. The fruit unquestionably became wet, yet he has no wish whatsoever for it to be wet; the water is nothing but a hiding place. That is not the act of a man who is machshiv the water upon his fruit.
The mishnah records an episode: "ma'aseh b'anshei Yerushalayim shetamnu d'veilaseihen bamayim mipnei hasikarin, v'tiharu lahem chachamim." Residents of Yerushalayim once sank their pressed fig cakes beneath water so that the sikarin should not find them. Just who these sikarin were is not fully clear: possibly plain bandits, possibly a faction operating inside the city that was destroying stores of food. The Chachamim declared those figs tahor. True enough, the owners themselves lowered the fruit into the water by hand, yet wetness was never what they were after, and consequently no hechsher took place.
The closing case rests on the identical logic. "Hanosein peirosav b'shibolet hanahar": someone sets his produce down into the flowing channel of a river, "l'havi'an imo," so that the water should carry the fruit along while he travels alongside it. Unable to manage the load himself, he lets the stream do his transporting for him. Once again he is the one placing produce into water, and the produce most certainly becomes soaked, yet that soaking holds no value for him in the least; the current merely takes the place of his shoulders. Water of this sort is not b'chi yutan, and the fruit is not rendered machshir l'kabel tumah.
With this case, the first perek of Machshirin comes to a close.