Kelim, Chapter Eight, Mishnah Ten
This mishnah deals mostly with the purity of food or liquids that are found in a person’s mouth.
1) If a person who came in contact with one who has contracted corpse impurity had (food or) liquids in his mouth and he put his head into the air-space of an oven that was clean, they cause the oven to be unclean.
2) If a person who was clean had food or liquids in his mouth and he put his head into the air-space of an oven that was unclean, they become unclean.
3) If a person was eating a pressed fig with impure hands and he put his hand into his mouth to remove a small stone:
a) Rabbi Meir considers the fig to be unclean
b) But Rabbi Judah says it as clean.
c) Rabbi Yose says: if he turned it over [in his mouth] the fig is unclean but if he did not turn it over the fig is clean.
4) If the person had a pondion in his mouth, Rabbi Yose says: if he kept it there to relieve his thirst it becomes unclean.
Section one: When a person comes into contact with another person who has contracted corpse impurity, the second person contracts first degree impurity. The liquids that he has in his mouth are impure. If he puts his head into an oven (not sure why one would do this, but let’s just forget about that for a moment) the liquids cause the oven to be impure. This is because liquids can defile vessels. The person himself, who has first degree impurity, does not defile the vessel, because people don’t defile vessels unless they have a higher form of impurity. We should note that Albeck explains that the word “foods” is not really relevant here because only liquids defile vessels. Foods cannot. The word “foods” is, however, relevant in the subsequent clauses.
Section two: If a pure person has pure food or liquid in his mouth, and he puts his head into an impure oven (didn’t learn the first time) then the food or liquids are defiled by the oven.
Section three: This person’s hands are impure, although the rest of his body is not (this is a concept which we will deal with when we learn Tractate Yadayim). If he puts his hand in his mouth to take something out, and at the same time he has a fig in his mouth, Rabbi Meir considers the fig to be impure. His hands defile the spit in his mouth, and it in turn defiles the fig. Rabbi Judah disagrees because he holds that the spit in his mouth is not considered to be a liquid. Rabbi Yose says that the spit in his mouth is considered a liquid only if he moved the fig around in his mouth, thereby uprooting the spit from its original space. In other words, if one gathers up his spit, it is considered a liquid and is susceptible to impurity, but the mere moistness of his mouth is not.
Section four: Rabbi Yose has another qualification for when spit can be considered a liquid. If he has a small coin, a pondion, in his mouth in order to cause him to salivate and thereby feel less thirsty, then his spit is considered to be a liquid and it can be impure.
As an aside, I have heard of people putting small stones in their mouths on fast days. They say it helps one get over being thirsty.