Shulchan Arukh Orach Chayim · Siman 438

English

[The Laws that Apply when] a Mouse Enters a Place that was Previously Searched with a Loaf in Its Mouth, 2 Seifim If a mouse enters a house that has been checked, carrying a loaf in its mouth, and one enters after it, and one finds crumbs, even if enough crumbs to constitute the entire loaf, one must return and inspect the house after the loaf that the mouse brought in, as it is not the nature of a mouse to break up bread, and these crumbs likely came from elsewhere and not from that loaf. However, if a toddler enters a house carrying a loaf in its hand, and one enters after it, and crumbs are found, there is no need to return and inspect, assuming that the toddler ate, and these crumbs fell from it during eating, as it is the toddler's nature to break up bread. Some say that if the crumbs do not amount to the entire loaf, one must still return and inspect. The laws concerning a mouse entering and leaving were omitted by the Rabbi since they are uncommon

English

If there is a size of an olive of leaven on the roof, one is obligated to bring a ladder to remove it, as sometimes it may fall from the roof. But if the leaven was in a pit, one is not obligated to bring it up, rather they nullify it in their heart, and it is sufficient.