Mishnà su Levitico 11:38

Any liquid which was desired at the beginning though it was not desired at the end, or which was desired at the end though it was not desired at the beginning, comes under the law of "if water be put." Unclean liquids render unclean whether [their action] is desired or is not desired.

If one shook a tree and it fell on another tree, or a branch and it fell on another branch, and under them were seeds or vegetables [still] joined to the ground: Bet Shammai say: this comes under the law of ‘if water be put’. But Bet Hillel say: this does not come under the law of ‘if water be put’. R. Joshua said in the name of Abba Yose Holikofri a man of Tivon: Be surprised if there is any liquid that according to the Torah causes susceptibility to uncleanness except one put it on with intention, for it is said: "If water be put upon the seed."

If one shook a bundle of vegetables and [water] dropped down from the upper [side] to the lower [side]: Bet Shammai say: this comes under the law of ‘if water be put’. But Bet Hillel say: this does not come under the law of ‘if water be put’. Bet Hillel said to Bet Shammai: if one shakes a stalk, do we fear lest water drops from one leaf on the other leaf? Bet Shammai said to them: a stalk is only one, but a bundle has many stalks. Bet Hillel said to them: behold, if one lifted a sack full of produce and put it beside the river, do we fear lest water drops from the upper [side] to the lower [side]? But if he lifted two sacks and placed them one upon the other, the lower [sack] comes under the law of ‘if water be put’. Rabbi Yose says: the lower [sack] remains insusceptible to uncleanness.