According to his words, regarding our case, we decide that chametz (leavened bread) is forbidden to derive benefit from, as is written in the Shulchan Aruch (Code of Jewish Law, Orach Chayim 486:1): "Chametz from six hours and onwards on the fourteenth day [of Nisan] is forbidden to derive benefit from." It seems that nullification in one's heart alone should suffice, so it is puzzling why we need to specify verbally. As we mentioned earlier, it is necessary to articulate and understand what we are saying, and without doing so, the chametz is not nullified, and one transgresses the prohibitions of "not seeing" and "not finding" chametz.