Pesachim 9 - Weasel drags bread from house to house
After one searches his home for chametz, he does not have to worry that perhaps a weasel will now bring bread from another house. The same is true of one's room: once it is searched, one need not think that a weasel might bring it there from another room. This is true because if one is to be concerned, he would have to suspect that a weasel brought it from another courtyard, or another town, and there would be no end to his worries.
However, as the Talmud notes, this rule is good only if one does not see a weasel or a mouse, going into his house with bread. If he does, then he has to be concerned. But why? Why not say that the mouse ate that bread?! After all, we have multiple ruling which assume that if a mouse or a weasel are found in a place where possibly ritually impure meat was dropped, then it was surely eaten, and the place is therefore ritually clean!? - True, they will eat the meat, but as for the bread, they will leave some over and hide it.
And yet, we do worry about weasels, since all food left over after search for chametz is hidden and not put in an easily accessible place - obviously because a weasel may take it away. Abaye explained, "Yes, the weasel may hide it just before Pesach when soon there will be no bread available, but not earlier, when there is plenty." Rava objected, "Is a weasel a prophetess that she knows that soon there will be no bread?! - Rather, the danger is that the weasel will take it away in one's presence, and then he will have to search again."
Art: A Weasel by Edward Lear