I DON'T UNDESTAND THE GEMARA SAYING THE OWNER OF THE BREAD ILL NOT BE M'YAYISH BECUSE OF CISHUF GRANTE, A NOCHRI
MAY BELIEVE IN IT, BUT CAN A JEW?
In this Gemara, the Jew is not believing in the power of Kishuf. The Gemara is saying that a Nochri will not trample the bread because he, the Nochri, thinks that it was placed there by someone trying to perform an act of Kishuf. The Jewish owner of the bread therefore knows that wherever his lost loaf might be, no one will trample it and thus he does not have Yi'ush -- Nochrim won't trample it because they believe in Kishuf, and Jews won't trample it because of the requirement to act with respect towards bread and not step on it.
Y. Shaw