ופני המן חפוי
“Haman’s face was covered.” (Esther 7:8)
The Ibn Ezra explains that the custom in Persia was, that if the king was angry at a certain person, they would cover over his face, this is what the pasuk means: ופני המן חפוי, the king was angry with Haman, therefore, he had his faced covered.
However, the question is, why do we need to be taught this in the Megillah?
The Brisker Rav explains: Charvonah was one of the low-end ministers of the king, like we find that at the beginning of the Megillah he is listed very low down on the list. Being that he was low down, he was too scared to speak up against Haman, who ranked top of the list as he was scared that he would take revenge. However, now that Haman’s face was covered over, and the king was angry with him, he was no longer scared, therefore, this time he plucked up the courage and spoke against him.