Well, if the Hemlock Grove star had managed to flash the smile his incarnation has now made infamous among those who fear it, then even the most staunch doubters would have fallen in line. And Skarsgard detailed just how he came up with that smile on a recent Conan appearance, saying:
Read more at HollywoodReporter
Well, it's a funny story cuz my older brother Gustaf, who is an actor as well, he had this ability to point his lip in a very strange way. And for some reason---I dunno how I understood that I could do it as well---but I was maybe 10 years old and I'm like [does the Pennywise smile]. I came up with this character. I would pull my t-shirt over my head so you would just see the opening. I would do [The IT] face, and then I would chase my little brother and scare him.