Gabriel's cheery HI! when pulling Rachel away from death. The fact that he looks like an undead version of, well, Christopher Walken makes it that much funnier.
Then a Genius Bonus joke as Gabriel is teaching kids to play his horn. Keep in mind, it is the horn that Gabriel's supposed to blow to begin The Rapture. Not surprising when one boy shatters his schoolhouse's glass windows with it.
Made funnier by his benediction to the departing children: "Study your math, kids. Key to the Universe."note Which priest/scientist Roger Bacon originally stated, that mathematics was the lock and key to the Universe.