Every Purim Jews congregate to listen to a reading from a book called the Megilah which features the backstory of Purim. It’s the most outwardly religious part of Purim. The congregation is encouraged to be active and loud, reacting verbally to every single mention of the characters’ names in the story. Mordecai and Ester (the Jewish heroes) get jubilant cheers every time their name is read while the bad guy Haman is booed. The congregation is even traditionally encouraged to drink so much that they can’t tell whose names to boo or cheer.
Again, this is the religious part of Purim but the encouragement to chime in makes it stand out from other Jewish holidays in a way that fits the extra cheerful celebration of Purim. While this folklorist’s congregation doesn’t drink during the reading, it does fit the rest of the relatively lax nature of the event.