Mischna zu Bamidbar 19:12

If one ate unclean foods or drank unclean liquids and then he immersed and then vomited them up, they are still unclean because they did not become clean in the body. If one drank unclean water and immersed and then vomited it up, it is clean because it became clean in the body. If one swallowed a clean ring and then went into the tent of a corpse, if he sprinkled himself once and twice and immersed himself and then vomited it up, behold, it remains as it was before. If one swallowed an unclean ring, he may immerse himself and eat terumah. If he vomited it up, it is unclean and it renders him unclean. If an arrow was stuck into a man, it blocks so long as it is visible. But if it is not visible, he may immerse himself and eat terumah.

How does one harvest the grapes of a bet peras? They sprinkle [hatat water] on the harvesters and the vessels [once] and then a second time. Then they harvest the grapes and take them out of the bet peras. Others then receive [the grapes] and take them to the winepress. If the latter set [of persons] came into contact with the former, they become unclean, This is according to the words of Bet Hillel. Bet Shammai say: [the gatherer] holds the sickle with sinew-rope, or harvests the grapes with a sharp flint, lets [the grapes fall] into a basket, and then he takes [them] to the winepress. Rabbi Yose said: When do these rules apply? [Only] in the case of a vineyard which subsequently became a bet peras; but a person who plants [vines] in a bet peras must sell [the grapes] in the market.