Elijah the Prophet

At many brisses, two chairs are set up at the spot where the bris itself will take place. Ask the mohel, he'll tell you "One is for the sandak (who holds the baby during the bris), and the other is for Eliyahu Hanavi (Elijah the prophet)."

You're kidding, right?

No. The tradition to have a place set aside for Elijah at a bris is pretty old.