The outstanding teaser trailer for Andrés Muschietti’s film adaptation of Stephen King’s It was released yesterday, and it would be an understatement to say that people were impressed. One complaint that I kept seeing across the internet was one of disappointment in the fact that the blood flying out of Beverly Marsh’s sink was no longer blood, but rather some strange black liquid. Others believed that the liquid was blood but the filmmakers actively chose to make it black. If you were one of those people,* let me assuage your concerns. The liquid coming out of Ms. Marsh’s sink is most definitely blood, and it will be red when you see the film. It just can’t be red in the trailer.

When I got to see the trailer at the SXSW Conference and Festivals earlier this month, I mentioned that Muschietti warned us that the effects for the trailer hadn’t been completed yet, but I couldn’t tell what he was referring to. Everything in the trailer looked complete to me. It turns out he was referring to the blood exploding out of Beverly’s sink. In the version of the trailer I saw, the blood was still red. The studio had to CGI over the blood in order to make it black because the Motion Picture Association of America has very strict guidelines on what you can and can’t show in a Green Band Trailer (trailers with that green screen that shows before them that says “The following preview has been approved for ALL AUDIENCES by the Motion Picture Association of America”).

According to the MPAA’s Advertising Administration Rules, “Approved (Without Restriction)” forms of film advertisement may not include:

Realistic or excessive violence, brutality or scary images, including, but not limited to: depictions of blood or wounds; scenes of torture; dismemberments; mutations or mutilations of bodies (including cadavers); people in jeopardy, including images of people being abused, punched, beaten, bound or gagged; disturbing or frightening scenes, including some transformations and morphing particularly when a character becomes abnormal or grotesque; children in peril, including verbal or physical abuse of children; overt references to or scenes depicting death of a parent or a child; realistic depictions of natural disasters; intense depictions or threats from supernatural creatures or the occult; cruelty to animals; and people or animals on fire (except where, in the opinion of the Advertising Administration, the portrayal is clearly unrealistic to audiences, such as a comic book character).

What that description conveniently leaves out is one important descriptor: approved forms of advertisement (or “Green Band Trailers,” as you might know them as) may not include depictions of red blood. If it’s not red, then a small child won’t think it’s blood. This is why so many of the horror film trailers you see have black blood instead of red blood, and that also applies to the trailer for It. This isn’t the first time you have seen this in a movie trailer before. Just look at the blood trail left by the pitchfork in the trailer for 2010’s The Crazies or the blood-stained hospital mask of the infected girl in the trailer for the PG-13 film Carriers. You just can’t show blood in green-band trailers (red band trailers are another story).

Related: Here’s the Terrifying ‘IT’ Trailer in 50 Hi-Res Images!

Interestingly enough, the red blood rule also applies in some way to a film as a whole. For example, if a film contains a certain amount of red blood, it could face an NC-17 rating as opposed to an R rating (Wes Craven’s Scream ran into this issue back in 1996). Because of this, filmmakers have been finding creative ways to work around that rule. Think the Crazy 88 scene in Quentin Tarantino’s Kill Bill, or the entirety of Robert Rodriguez’s Sin City. Tarantino filmed The Bride’s (Uma Thurman) famous fight scene in black and white. Rodriguez filmed all of Sin City in black and white as well, and most of the colored blood was yellow (from the Yellow Bastard). Ignoring the fact that Sin City was going to be filmed in black and white no matter what in order to match the artistic style of Frank Miller’s graphic novel upon which the film is based, it’s a pretty clever loophole. If the blood isn’t red, then it’s not really blood! It’s a little silly when you think about it, but those are the rules.

So I hope this clears some things up for those of you who were worried about the mysterious black liquid. I can’t wait to check out It when it hits theaters on September 8th!

In the film, seven children known as The Losers’ Club come face to face with life problems, bullies, and a monster that takes the shape of a clown called Pennywise.“

Bill Skarsgard stars as Pennywise, the sewer-dwelling monster.

The members of the modern Losers’ Club will be portrayed by Jaeden Lieberher (as Bill Denbrough), Finn Wolfhard (as Richie Tozier), Jack Dylan Grazer (as Eddie Kaspbrak), Wyatt Oleff (as Stan Uris), Chosen Jacobs (as Mike Hanlon), Sophia Lillis (as Beverly Marsh) and Jeremy Ray Taylor (as Ben Hanscom).

The Leper will be portrayed by Creature performer Javier Botet, and the trio of bullies who torment the Losers’ Club will be portrayed by Nicholas Hamilton (as Henry Bowers), Owen Teague (as Patrick Hocksetter), Logan Thomspn (as Victor Criss) and Jake Sim (as Belch Huggins).

Dan Lin, Roy Lee, Seth Grahame-Smith, David Katzenberg, and Barbara Muschietti produce.

*I understand that many readers probably understand the difference between a green- and red-band trailer but this post is for the readers that don’t understand that. Please be kind to them in the comments.