***WARNING: The following will contain a significant spoiler for the film Pacific Rim: Uprising and minor spoilers for a lot of other films***

There’s a character in the film who is possessed by an ill-defined alien intelligence, and you know this because at one point he starts talking in a voice rougher and deeper than human vocal cords should be able to generate. This is an old trope, one dating back to The Exorcist at the very least, and like most such tropes it has become so familiar to genre fans that we no longer need it explained. It’s a kind of unmistakable shorthand, one we all can read.

It made me think of another kind of shorthand, one you’ll find in dozens of genre films and TV shows (and occasionally even in books). A visual convention that conveys instantly that a character is no longer in control of themselves. Specifically, when a character’s eyes change color, typically becoming one solid color, you know the character’s been taken over.

There’s some small real world basis for this. It’s true that sometimes when a person suffers a seizure, their eyes will roll upward in their head until only the whites can be seen. This doesn’t happen for all people with seizures but it is deeply disturbing to see when it does happen. Genre film creators, probably since the dawn of cinema, have been using this visual cue to signify that a character has lost control of themselves. It’s been used so often that it’s actually generated a series of corollaries, each of which send their own message:

• All White Eyes: When a character’s eyes cloud over and turn white it means they’ve become a mindless shell of themselves. You see this a lot in zombie movies. Occasionally you’ll also see it in stories about hypnosis, though more often they’ll use:
• Eyes Closed at Inappropriate Times: A character walking around with their eyes closed is most likely sleepwalking, but it can also represent that they’ve entered a dream world or simply that they’re under mesmeric control.
• Eyes Filled with Lightning: Almost always suggests that a character has been infused with some kind of otherworldly power, either by intentionally accepting it into themselves or having it imposed on themselves by an ancient/alien artifact, etc. A more modern version of this is when a fiery orange glow can be seen in the character’s eyes (see Iron Man 3).
• Reptilian Eyes: The character is a doppelgänger or a shape-shifter; they may be able to hide the slit pupils and golden sclera behind a nictitating membrane (somehow) or this may be the only sign we get of their alien nature. This was not original to V but it certainly used the trope to great effect. Bonus points if other characters don’t notice the weird eyes until it’s far too late.
• Pupils Dilate/Contract Suddenly: Typically this means a character is under the effect of a powerful drug, or has had a moment of cosmic epiphany. The fact this happens to everyone when they enter a suddenly dark or bright room is almost never shown in film and TV.
• Unblinking Eyes: Often combined with a staring, intense gaze that conveys a character is inhuman or at least mentally deranged. You don’t see this one as much as you used to, though it popped up in one of the Harry potter films.
• Eyes Change Color: Very rare, but occasionally you’ll see this used as shorthand for a character who suddenly and magically becomes far more attractive than they used to be, such as when they are reborn as a vampire (Interview with the Vampire uses this, I’m pretty sure–I would have to go back and rewatch the movie to make sure. The Craft definitely has a scene of this).
• Eyes Turn Solid Black: The character has been possessed by Ultimate Evil. Satan, Lucifer, or some malign Lovecraftian alien intelligence, maybe. Also very rare–and incredibly striking when you do see it. Interestingly, you also occasionally see this one used to show that a character is magically observing the world through the eyes of an animal.

Honorable Mention: Maybe the best use of this shorthand I’ve ever seen was in the movie Lucy. I have a lot of problems with that film, but there’s a wonderful sequence where Lucy’s eyes change color, then turn reptilian, then bird-like, and so on. It’s a very quick scene but it manages to convey that the main character is recapitulating all of biological evolution in the span of a few eye blinks. It’s brilliant because it gets its message across with no dialogue and most people who see the scene understand what it’s saying without exposition.

Like any kind of nonverbal cue, when you use these things as shorthand they’re fine–in fact, they immediately signal to the viewer that they are in familiar genre territory. But when they’re done in interesting, innovative ways they become the true essence of art.