Editor’s note: The below contains spoilers for the IT: Welcome to Derry finale.

Stephen King‘s IT is regarded by many as his scariest work thanks to its villain, a killer clown named Pennywise. However, this monster is something more than a simple man in makeup who likes to kill kids. Instead, the clown is one form of a shapeshifting alien entity that’s thousands of years old. In Andy Muschietti‘s IT: Welcome to Derry, more of Pennywise’s (Bill Skarsgård) mythology is explained, such as how the clown persona was taken from a real man named Bob Gray, but what’s going on when its jaws go wide, and three bright lights paralyze its victim, causing them to float off the ground?

The Deadlights Are Shown Often in ‘IT’ and ‘Welcome to Derry’

The Deadlights are shown in King’s novel and the 1990 miniseries, but nothing matches the visual and audio reveal of them in the 2017 film adaptation of IT, when Beverly Marsh (Sophia Lillis) is confronted by Pennywise in the sewers. When she tells the clown she’s not afraid of it, Pennywise’s jaw detaches, peeling back over its head and showing off rows of teeth, while a chilling bass drop in the score amplifies the terror. In its throat are three small but intense lights, which instantly turn Bev’s eyes white, putting her in a trance that causes her to float from the ground. They’re also seen in IT: Chapter Two, when Richie Tozier (Bill Hader) is caught in their spell.

The Deadlights appear several times in IT: Welcome to Derry. Ingrid Kersh (Madeleine Stowe) encounters them when she realizes that the entity is no longer her father, as does Will (Blake Cameron James), his father Leroy (Jovan Adepo), and the entire underclass of Derry High School. We see how they work, paralyzing a victim, but what are they, exactly?

Andy Muschietti’s Deadlights Are Different From What Stephen King Created

The alien in IT and Welcome to Derry is an entity that crash-landed on Earth inside of a fallen star thousands of years ago. Since then, it has slept under the earth in Derry, Maine, but every 27 years it surfaces to feed on the fear of its victims, taking the form of what they fear most, which is why we often see it as a clown. The clown has a kryptonite of sorts, with it being afraid of a dagger made from the star, and the cage that keeps it confined to Derry is made out of pillars formed from the same star. But what makes this even more difficult is that humans can’t exactly see what they’re fighting against unless it reveals itself, because the alien doesn’t have a body as we know it.

In essence, the Deadlights are the true form of the entity — a bright, abstract energy. This is why, after Pennywise is defeated at the end of IT: Welcome to Derry and is sent back to sleep for 27 years, its previous forms peel away, leaving only the small balls of light which scatter and zigzag away like embers.

Those Deadlights, which are beyond anything a human can comprehend, can also be used as a weapon. In Stephen King’s novel, they drive a victim insane and remove their soul, but in Andy Muschietti’s films and series, Pennywise breaks them out when its prey doesn’t show any fear, seen in its interactions with Bev Marsh and Richie Tozier in the IT films as well as Will Hanlon, his father Leroy Hanlon, and Ingrid Kersh in IT: Welcome to Derry.

If you’re not afraid of Pennywise, it’ll simply paralyze you with the Deadlights — or, in the case of Derry High School, the Deadlights come out because it’s easier for the entity to put the students in a trance first to transport them to the sewers, then feed on them later. However, when the Deadlights’ hold is broken in Andy Muschietti’s IT and Welcome to Derry, its victims are shaken from the trance but ultimately okay. The entity can show them visions in the Deadlights as well, such as when Beverly, in IT, tells the Losers Club that she saw a vision of the future where they fought the entity again as adults.

Other Stephen King Novels Have Referenced the Deadlights

Image via Warner Bros.

IT isn’t the only place where the Deadlights have come up. They also appear in another part of Stephen King’s world, The Dark Tower series. The main villain in those books is the Crimson King, who can change forms, and tries to destroy the Dark Tower in the titular novels. The weapon of the Crimson King is the Deadlights, a force it wields to destroy everything in its path.

The Deadlights can be confusing to understand, which is fitting, since they are described as being impossible to comprehend by humanity. In IT: Welcome to Derry, seeing them is like looking into the true face of an eater of worlds. There is no way to resist them, however, and they paralyze their victims every single time. If you’re entranced by the Deadlights, your only hope is that someone is fighting beside your side and can help break the spell. With two more seasons of IT: Welcome to Derry promised, we definitely haven’t seen the last of the Deadlights. In 1935 and 1908, Pennywise will return and show its true self to the bravest of souls. Whether they can be as lucky as the likes of Beverly, Richie, or Will and Leroy Hanlon remains to be seen.