Eyes Never Lie

"Then one day Strangefolk arrived in the town.
They came in camouflage, hidden behind dark glasses, but no one noticed them: they only saw shadows.

You see, without the Truth of the Eyes, the Happyfolk were blind."

—Gorillaz, "Fire Coming Out of The Monkey's Head"

The suggestion that if you stare into someone's eyes deep enough, you can glimpse their true nature.

It's well known that the eyes are the "windows to the soul"—in fact, it's mentioned in perhaps half of the Eye Tropes we have. What does that actually mean? Well, in effect, it generally means that looking into one's eyes can give one insight into what the person is thinking. At the very least, it can betray some level of emotion, and some even believe one can tell truth from lies, and determine the true nature of one's personality, simply by employing this method.

There is some truth to this. It is possible to glean some aspects of one's thought process by means of eye contact. This is mainly because of subtle cues in facial expression, most of which are centered around the eyes and brow. These cues are extremely difficult to master, and so even a very accomplished liar has difficulty fooling a person who has learned to recognise them.

Nevertheless, the fact remains that the eyes are not so much windows to the soul as gel-filled orbs with clear lenses designed to see with, and as such many savvy writers of the modern age have subverted this trope with characters whose motives cannot be so easily read.

But, in the world of fiction, matters go beyond merely distinguishing lies and feelings. Some tales, especially fantasy, associate special traits to the eyes which tell other characters and, more importantly, the reader more about the character who bears them. Most Eye Tropes, ranging from Technicolor Eyes to the likes of Blinding Bangs, serve in this capacity, if primarily on a metaphorical level.

Some very common subtypes:

You can read your opponent's intent in combat, giving you time to prepare for their next move and revealing feints.
You can detect lies this way. Lovers will know that the others' feelings are true after their eyes have met.
If a character is transformed, looking them in the eye will still let you know that it is them. (Can be a form of Red Right Hand for the audience.) Some characters will intentionally hide these behind Opaque Lenses, Scary Shiny Glasses, and Sinister Shades.

Truth in Television: when people see something that they really like/want, their pupils dilate. For example, a family member, loved one, potential mate, precious jewels, etc. And involuntary eye movements can give a clue about a person's mood or what they may be thinking. (Hence the cultural custom of asking people to look into your eyes when you think that they may be lying, and why keeping eye contact is considered in many cultures to be a sign of politeness and honesty.)

Occasionally a visual tool too: we see a close-up in the characters and a picture of what they are appears inside the iris. Compare Reflective Eyes and The Shadow Knows.

Examples of Eyes Never Lie include:

Anime and Manga

In Angelic Layer, one of Misaki's opponents was able to anticipate all of Misaki's Angel's attacks by watching her. Once Misaki figured this out she was easily defeated.
In Apollo Justice: Ace Attorney, Apollo uses his bracelet to see through Machi's eyeglasses during a trial to determine that he's lying.

Comic Books

Judge Dredd: By the conclusion of "The Judge Child Quest", Dredd has reason to believe that The Judge Child is not all he appears to be, so Dredd looks into his eyes to see if he finds someone who is misguided or a creature of malice. He only sees evil.

Film

Blade Runner: Replicants don't have human-normal eye reactions to emotion-provoking situations. Rather than helping them lie, the lack of reaction is a vulnerability, marking them as a replicant.
In The Negotiator, Danny Roman (Samuel L. Jackson) delivers a lecture on facial cues, specifically touching on the tendency of the eyes to look toward the upper left when accessing memory and to the upper right when accessing imagination and making something up.
In the 2005 film The Island, after the duo escape from the cloning organ facility they once believed to be their sanctuary and home, while watching TV the heroine is somehow able to tell that the news reporter is lying about the events they just experienced due to the expression of her eyes.

Literature

In The Anubis Gates, Beth Tichy recognizes a monster as her fiancé, transformed, by the expression in his eyes -- just after she shoots it.
Discworld
- In The Colour of Magic it's stated that gods, no matter how else they may transform themselves, are unable to disguise the true nature of their eyes.
- A similar rule applies to the various transformed creatures in Witches Abroad. For example Greebo, a witch's evil-minded cat, is transformed into a human. As a human he still has the glowing, slitted eyes befitting a cat.
- Experienced conman Moist Von Lipwig of Going Postal notes that he likes the sort of person who looks in one's eye to see their true self, and has a whole gallery of true selves to show them.
- Night Watch plays with the trope: it's noted that unwavering eye contact can make a confident liar stick out.
- Slightly more inexplicably, Snuff proves that Vimes can also identify a murderer by eye contact. Because he recognises in their eyes the same thing he sees in his own reflection.
The Dresden Files: Wizards can read the intimate details of any person's soul just by looking into their eyes, which is called a soulgaze. It has its limitations, though-- It Only Works Once, and the target gets to see the exact same things about the wizard. Also it's stressful at best, and can cause a person to Go Mad from the Revelation at worst, especially since one can never ever forget what they see. Wizards tend to avoid making eye contact unless they have a damn good reason to do otherwise.
In Good Omens, the demon-in-human form Crowley adopts a stylish persona, including Cool Shades that he wears all the time (and gets mocked for by another character). Near the climax, he loses the shades, and it's revealed that at least part of the reason he wore them was that even in human form he still has his real eyes.
All over the place in the Honor Harrington series, where stoic naval officers with otherwise perfect poker faces give away their inner worries or kindness (e.g. Honor Harrington herself), and sociopathic villains give away the hollowness inside.
The Man Who Was Thursday plays with the "wearing Sinister Shades to disguise his true nature" version of the trope, with a sinister character whose dark glasses prompt speculation about what horrors his eyes would reveal if they were visible. Ultimately, it's revealed that not only are his eyes entirely normal, they proclaim his true -- kind and friendly -- disposition, so he had to hide them in order to appear sinister.
The Moomins: In one Nightmare Fuel-worthy scene, the characters find a magic hat that transforms things. Moomintroll tries it out of curiosity and is turned into a hideous monster. None of his family members recognize him, but in the end Moominmamma can still tell that it is him by staring into his eyes.
Harry Potter and the Prisoner of Azkaban: Harry doesn't believe Sirius Black about his parents' murder until Black, in tears, looks Harry in the eyes and tells him the exact details.
- Throughout the series, Harry is said to "Look a lot like your dad, but you have your mother's eyes." Later in the series, we find out that Harry's resemblance to his father is mostly superficial (physically and personality-wise), and that ultimately, he is much more like his mother.

Live-Action TV

An episode of Buffy the Vampire Slayer invokes this when Giles is turned into a demon; Buffy recognises him by looking him in the eyes and noting that no one else could look as annoyed with her. Lampshaded when Buffy suffers a Grand Theft Me later on.

"Giles, you turned into a demon and I knew it was you! I mean, can't you just look in my eyes and be all intuitive?"

Lie to Me: Dr. Cal Lightman and the rest of the Lightman Group use microexpressions (a minute form of facial movements) and body language to determine whether or not someone is telling the truth. Cal, Gillian, and Loker studied for years to learn it. Torres is a "natural", one of something like 5% of the population who has the ability to spot deception.
On NCIS Kate claims she could tell if a person was good by looking into their eyes, but was not very good at it as she accidentally helped a bomber blow up the place where she had worked, then let the terrorist who later tries to kill her go because there was good in their eyes.
Doctor Who: River looks into the Doctor's eyes for this reason in the finale of Season 6.

Music

Stephen Foster's song "In The Eye Abides The Heart".
"Fire Coming Out of the Monkey's Head" by Gorillaz takes it to an extreme: the Happyfolk are so dependent on the "Truth of the Eyes" that they are unable to even see people with covered eyes. It's probably a metaphor for dangerous innocence.

Tabletop Games

Subverted in Legend of the Five Rings—one of the Scorpion samurai mentions that lying with their eyes is one of the first things the youth learn in his clan.

Video Games

In Fire Emblem: Blazing Sword, Wallace declares Lyn trustworthy and joins her cause after getting one good look of her eyes.

Wallace: I've been a knight for 30 years, and there is one thing I learned. A person with eyes as bright and true as yours is no deceiver.

In Metal Gear Solid, Snake tells Meryl that she never shot someone from the way her eyes constantly wander off.

Web Comics

In The Order of the Stick this becomes a plot point. Blind Pete is able to betray Haley because she relies upon this to sense motivations.

Western Animation

Disney's Beauty and the Beast—that's how Belle realizes that skinny prince is really her Beast.
In Codename: Kids Next Door the characters can distinguish between their friends and their friend's evil counterparts from the Mirror Universe by looking into their eyes.

Eizzil: How did you know I wasn't really your stupid girlfriend?
Nigel: When I look into Lizzie's eyes, I can tell she's not a jerk.

Subverted in The Emperors New Groove. Pacha refuses to make a deal with Kuzco unless he looks him in the eye and means it. He fails to notice that Kuzco is playing him for a sucker until he's hanging above a chasm.
In Rango, Rattlesnake Jake says that Rango won't shoot him because he doesn't have a killer's eyes. In round two, Jake gets an Oh Crap moment after Rango has had his act together and is willing to kill.
Subverted in The Simpsons.

Homer: Look me in the eye boy, and tell me you didn't do it.
Bart: I didn't do it.
Homer: Why you little...!
Throttles Bart
Homer: How dare you look me in the eye and lie like that!

Real Life

While not foolproof by any means, eye movements and how someone looks at you can often be an indicator if they are lying to you or not. However, skillful liars can control this to an extent.