Minor spoilers for the It novel and film below!
It shouldn't be a surprise to anyone that the latest film adaptation of Stephen King's It is full of horrifying moments. The funny thing is, Pennywise, the demonic clown stalking the group of young misfits (aka the "Losers Club") in Derry, ME, is only the tip of the blood-soaked iceberg. One of the more disturbing lines of the film is one repeated by Pennywise and the gruesome hallucinations he makes the Losers Club encounter throughout the film: "They all float down here. You'll float, too." So, what exactly does this creepy-as-f*ck line of dialogue mean, exactly?
"They all float down here. You'll float, too."
Chapter one of the two-part story, which already has its sequel in the works, doesn't give an explicit explanation as to what the phrase means, just as King never comes out and says exactly what it means in the book, either. The simplest and most obvious interpretation is that all the talk of floating is a reference to the fact that Pennywise (aka the titular "It") murders his victims and drags them down to the town's sewer system where he dwells, which is full of water. And what do dead bodies do in water? That's right — they float.
There's another way to look at the chilling line, however. Though It frequently appears as Pennywise (and other horrific creatures), it's actually a manifestation of an otherworldly power from an alternate plane (a dark, empty space between dimensions) that appears in other King books, like The Dark Tower. Perhaps when It drags you down to the sewers and has you for lunch, your soul is stuck in this same place — not heaven, not hell, but floating in some kind of weird limbo where It can take over whenever it wants. After all, we see Bill's dead brother, Georgie, pop up a few times throughout the movie even after his grisly death in order to taunt his older sibling.
It should be noted that, as we see at the end of the new film, It has the corpses of the missing kids somehow floating high up in the air within a chamber above his lair filled with junk he's stolen from the town. The bodies are literally floating, just as It promises all of the victims they eventually will. Apparently we'll have to wait until the second chapter of the film for any further explanation.