By now, you know: if a bunch of celebrities appear onscreen in a box configuration, a delightful a cappella song is about to happen.
Here's the Tonight Show's latest take on the format, with Jimmy Fallon, The Roots, Paul McCartney and the cast of Sing -- Reese Witherspoon, Matthew McConaughey, Scarlett Johannson and Seth MacFarlane -- teaming up to perform "Wonderful Christmastime."
Bonus: some animated animals even make an appearance.
