Yeah, the Wikipedia article for the episode [
https://en.wikipedia.org/wiki/Graveyard_Shift_(SpongeBob_SquarePants)] tells how the reference came about:
Episode writer Lender proposed to have Count Orlok of the 1922 silent film Nosferatu appear as a gag at the end of the episode. Series creator Stephen Hillenburg accepted Lender's proposal and allowed him to do it. Lender said, "Steve gave you the opportunities to do things that would really be memorable, if you could sell him on it." Lender then searched for books with scannable pictures of Count Orlok. However, the image of Count Orlok used in the episode was taken from the Internet. He said, "I searched what little there was of the Web back then." Nick Jennings Photoshopped the smile on Count Orlok to make sure it matched Lender's board drawing. Lender said, "It was my baby, and I held its hand until we shipped it overseas [to Rough Draft Studios in South Korea]." Before his idea of Count Orlok, Lender thought of "Floorboard Harry", a deleted gag that concludes the broadcast episode, in which he initially flickers the lights.
Pretty cool if you ask me. :cool:
In fact, I should add more about the actual film itself. You can read all about it here:
https://en.wikipedia.org/wiki/Nosferatu. For its time it was really quite groundbreaking. Roger Ebert, in a retrospective review, sums up the legacy of the film quite nicely:
Here is the story of Dracula before it was buried alive in clichés, jokes, TV skits, cartoons and more than 30 other films. The film is in awe of its material. It seems to really believe in vampires. ... Is Murnau's "Nosferatu" scary in the modern sense? Not for me. I admire it more for its artistry and ideas, its atmosphere and images, than for its ability to manipulate my emotions like a skillful modern horror film. It knows none of the later tricks of the trade, like sudden threats that pop in from the side of the screen. But "Nosferatu" remains effective: It doesn’t scare us, but it haunts us.