Pesachim 45 – Dough in the cracks of a kneading trough

It is normal to have some dough stuck in the cracks of a kneading trough. If the amount of this dough is more than an olive volume, one must dispose of it for Passover. However, if it is less than an olive, then it is considered nullified due to its small size, and one can keep it there.

There are qualifications to this rule, though: it is only applicable to the trough's upper part, which does not hold water. The bottom part of the trough, where kneading takes place and where water enters, needs to be strong, so there even larger dough pieces are used to strengthen the trough, and therefore they don’t have to be removed.

The same rule applies to ritual impurity: if one cares that the dough is there, it stops impurity. However, this statement is not easy to understand: if anything, it is not the same. Before, all depended on the dough piece's size, and now it depends on one caring about the dough being there. The Talmud tries to give it a few interpretations and ends up understanding it as thus. If the dough is important in his eyes, such as on Passover when chametz is prohibited, it serves as a separation between the possible impurity source (such as a dead rat) and the trough. On all other days of the year, it depends upon his caring about it: if he objects to the dough being there, then it is not part of the trough. Therefore, it separates the trough impurity. If he does not mind the dough being there, it becomes as if part of the trough, and if a dead rat touches this dough, the whole trough becomes impure.

Art: Alexandrine Rat and Black Rat by Archibald Thorburn