Bill Skarsgard on the set of "It."

With his girlfriend, Alida.

Skarsgard was deliberately sequestered from the rest of the cast to ensure that they would be as scared of him as possible. This broke his heart, since one of his favorite aspects of filmmaking is fraternizing with the cast and crew.

The first time the background child actors saw him, the director, Andy Muschietti, opened a door behind which Skarsgard stood in full costume and makeup, and he began terrorizing them in character. he is 6'4", so he towered over them.

The children ranged in age from 7 to 13 years old. Some laughed at first, some drew back from him, and one boy of 7 immediately started shaking when he saw Pennywise. Skarsgard said later, "I could tell that kid had coulrophobia, even if he didn't know it, so I focused on him for about 10 minutes."

Skarsgard drooled, snotted, growled, crabwalked backward, spoke in Swedish, spoke Swedish backward, and laughed maniacally in the children's faces for 10 minutes.

By the time he was done, every child in the room was crying, and the boy who was shaking had pissed himself.

He decided that if his performance could make a young child piss himself, he should reproduce it exactly in the film, and the above gif is what he did to the 7 year old boy.

Bill Skarsgard's "Pennywise" smile may actually be creepier without the makeup.

He did not come out of character around them until the film wrapped, whereupon he immediately wiped his makeup off with a wash cloth, took his costume top off and apologized to all of them, assuring them that it was all just an act and he was never going to hurt any of them.

He stated that he had nightmares every single night because he went to sleep in his trailer still in character and dreamed of himself actually eating the other actors.