I was on a flight from Austin - Houston - Kansas City on 12/20. At the end of the first leg, we were waiting to pull into the gate after landing. On the right side of the plane were four fire trucks and other emergency vehicles, all lights flashing. Fireman were hosing down the plane. The captain pointed out what was happening, perhaps thinking the passengers might be concerned. I think the phrase he used was "Spraying the Plane", and explained it is a customary ritual when a captain is retiring upon pulling into the gate on his final flight.
We are by nature ritualistic.