He was trying to cast one of Mohammad's spells on her to make her shut up. Muslims have practiced sorcery since Muhammads time, and of cource before that.
When the Crusades reached Jerusalem, muslim sorcerers stood on it's walls and shouted all sorts of magic spells at them.
Of course, they don't like to admit this dirty little Islamic secret. Mohammad mentions quite a few little sorcery tricks he used himself.