There is a custom that every time Haman's name is mentioned in the reading of the megillah, all the children (and many adults) set up a clamor. What is the origin of this custom?

The megillah mentions that Haman was "an Agagite," which, by tradition, means that he was a descendant of Amalek, the king who, taking advantage of the Israelites' weakness after having just left the slavery of Egypt, attacked them. The Torah thus commands us (Deut. 25:19), "You shall blot out the remembrance of Amalek from under Heaven." By banging on the ground or using the Purim gragger (rattle), we are figuratively "blotting out" the name of Haman, Amalek's descendant. Interestingly, there used to be a custom that when a Jew bought a new pair of shoes he would write the word "Amalek" on the soles. This way, whenever he took a step he was busy "blotting out Amalek."

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