Translation:Shulchan Aruch/Orach Chaim/432

1. The Laws Pertaining to the Blessing Recited Over the Search For Chametz, 2 Seifim:Before one begins to search for chametz, the blessing "אשר קדשנו במצותיו וצונו על ביעור חמץ" is said (and if one begins to check without making the blessing, he then makes the blessing) during the entire time that he has not finished checking (Kol Bo). One must be cautious that one not speak between the blessing and the beginning of the search. And it is a good thing not to speaking of other things until one finishes all of the search, in order that he may put his hear into checking in all the place that chametz may enter.

2. With one blessing, one can check several houses. And if the head of the household wishes, a member of his household should arise at the time he makes the blessing, and he should then spread out to check, each person searching his designated place, upon the conclusion of the blessing said by the head of the household. RAMA: It is our custom to leave small pieces of chametz in a place where the searcher will find them in order that his blessing not be in vain (Mahar"i; Ber"in). However, if one did not give [a piece to] and there is no mouse according to everyone the blessing "to obliterate" is said if it is found. (Kol Bo).