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Guarding the Chametz starting from the Bedika and onwards:
Prior to the Bedika, one must place all one’s known Chametz in an area that is not accessible to children or rodents. Similarly, any Chametz found during the Bedika is to be guarded, both during and after the Bedika, from being accessible to rats and children.
Not to enter or eat Chametz in the checked rooms without supervision: Once a room has been checked for Chametz, one must be careful to guard that no Chametz enter there, unless it is under strict supervision that no Chametz will escape. Those who are not careful and continue entering and eating Chametz in the already checked rooms without proper guarding and supervision that some of the Chametz does not escape, are doing a mistake and are to stand corrected.
How does one guard the Chametz: One guards the Chametz from mice and children by hiding it in a box, or other area that mice and children cannot take access. Alternatively, one can hang it in the air [on one’s ceiling, above the reach of mice and children]. Alternatively, one can place it by a high area which children cannot reach and place a wide vessel over it [so the mice cannot take from it]. However, a small, narrow vessel is no good being that the mice can overturn it and reveal the Chametz.
If one did not guard the Chametz: If one did not guard the Chametz and noticed that one of the pieces are missing, having been taken by children or mice, then one needs to recheck [his entire house] a second time. If, however, one is unsure if a piece is missing, such as he does not know the amount of pieces that were originally there, then he is not required to research the home. If one hid the Chametz properly and then found it to be missing , or even completely taken, he nevertheless does not need to recheck the previously checked areas.
Feeding Chametz to animals after the Bedika: One who desires to give Chametz to his animals to eat once the Bedika is done, must supervise them until they finish eating. One must supervise that they do not push and drag any of the Chametz to a hidden area. If there is any Chametz left over from what they ate, it must be removed.
Before the Bedika, one needs to guard from rats and children all known Chametz by hiding it in an inaccessible are. Similarly, any Chametz found during the Bedika is to be guarded both during and after the Bedika from being accessible to rats and children. If one did not do so, then if he knows that Chametz is missing from the Chametz, then he must recheck the house for the Chametz.
What is one to do if a family member or guests ate Chametz in the room after it was checked?
If the person was careful to guard the crumbs and clean up after himself, it is not necessary to perform another Bedika in the room.
 Admur 434:1-3
 Admur 434:2 “All the leftover Chametz which has remained at home for the sake of eating that night and the next day [or for the sake of burning or selling to the gentile], needs to be hidden/guarded from before one begins the Bedika.”
The reason: As if one were to not to do so, then there is suspicion that at the time of the Bedika itself, while one has checked one corner and has went to check another corner, perhaps he will see with his own eyes a mouse or a rodent taking some Chametz from the Chametz which he set apart to be eaten, and he will then need to recheck the corner which he had already checked for Chametz, as perhaps the rat dragged the Chametz that he took to the already checked corner. [Admur 434:2]
 Admur 434:1-2
The reason: When one checks for Chametz on the night of the 14th and removes it from the holes, cracks, hidden areas, and corners, and then gathers it all and leaves it in one area, [then since] he may not immediately destroy it and rather he must wait [to destroy] it until tomorrow at the end of the 5th hour as will be explained in chapter 445, he therefore needs to be careful with the Chametz and guard it from any of it being dragged away by children or mice. As if he knows that some Chametz was dragged away he will then need to recheck his house [as will be explained below]. [Admur 434:1] For the reason mentioned above, when one goes to search from corner to corner he needs to guard well the Chametz that he found in the previous corner and thus take it with him, or to hide it properly as will be explained. [Admur 434:2] The reason for why the sages required him to guard the Chametz [in all the above cases and did not allow one to take a chance of having it dragged away and then recheck the house for it] is because the sages suspected that one may forget to recheck, or perhaps he is not an expert in Halacha and does not know that he needs to recheck his house [for the missing Chametz]. Thus, the sages placed [an obligation] on every man to guard well the Chametz which he found by the search from being taken by children and mice. [Admur 434:1]
 Admur 434:3 “The world is only careful to hide the Chametz which they find during the search, however other Chametz [which they set aside to eat] they carry around everywhere within the already checked rooms, and are not careful to guard it from having some of it dragged away. Those who do so are not acting proper, and they need to be taught and warned against doing so.”
 Admur 434:1
 Admur 434:1
 The reason: As we suspect that perhaps the Chametz was placed in one of the holes of the house. [Admur ibid]
 Admur 434:5
The reason: If one transgressed and did not hide the Chametz at all, but rather left it spread around inside the house and was not careful to guard it then if he does not know how much Chametz was there, and it is thus possible that really some of the pieces were dragged away by children and rats, nevertheless, he does not need to recheck the rooms for Chametz. The reason for this is because since he is not certain that any Chametz is missing, we therefore do not require him to recheck the already checked areas do to the mere suspicion that perhaps a large piece of the Chametz was dragged by the mice and was placed in one of the holes of the house. As if we would require him to recheck his house because of this suspicion, then there is no end to the suspicions [and the Bedika will never be able to finish], as then we should also suspect that the [unknown] Chametz which still remains in the room of one Jew who has not yet finished the search, and most probably contains Chametz, may have been dragged by rats into another Jews house which has already finished the entire search, as it is impossible for all Jews to finish their Bedika at the same time. Thus, he would then have to recheck the entire house, and this then would repeat itself endlessly. [Admur ibid]
 Admur 434:4
The reason: As certainly a person has taken it from there and not children and mice. [Admur ibid]
 Admur 433:27
 The reason: It may not be left there for them to continue to eat, as perhaps the Chametz will remain there until after Pesach begins. Even if one plans to visit the area prior to the 6th hour to check if there is any remnant of Chametz that needs to be burnt, nevertheless, we suspect that perhaps when the time of burning the Chametz will arrive he will forget about the Chametz that he placed in front of them being that it will not enter his mind to suspect that there is any leftover Chametz. Therefore, at the time that he gives them the Chametz, he must not move from the area until they finish eating and he is then to remove the leftovers and hide them [to be burnt for the next day] as then he will certainly not forget to burn it, just like he does not forget to burn the rest of his known Chametz. [Admur ibid]