Sheep in the Big City Easter Egg - The Man Who Yells

Okay, this weird little guy appears 3 times.

The first and second sightings being in the pilot episode when the narrator is previewing the Big City, and you see this odd little man appear on the screen for a second and blink at you. Then in the scene where Sheep lands in the Big City and the narrator says "...and the yelling?" and the guy appears again screams at Sheep. (Did anyone but me find Sheep's little freak out just so kawaii? :))

And in the series episode "Going off the Sheep end", when Sheep gets plastic surgery and the Angry Scientist used the stink machine on the city, he appears again and just shouts at the audience.

Who is the guy? It's man who yelled, the star of Mo Willems' very first short film. You can still see it on Atom Films.