DUH-DOOOO EMMMMM!
This isn't a new trick for Zach, but definitely a different way of doing it.
Today I caught him looking at a moving box with letters on it. He was saying, "Duh-doo!" (that's W) then leaned way over until he was almost upside down and said, "Emmmmmm!" And just kept on swinging right-side up, then upside-down, so the "W!" would turn into an "M!"
He's a crack up!