This is when someone is alerted to danger behind their back by a conveniently placed, or ill-placed depending on what side you're on, reflective surface, whether an actual mirror, window, body of water or anything else that might have a reflection on it. This allows the mark to realize something's going on.
From there they have several options. Depending on whether the tail realizes they've been made, the mark might just act as normal to lull the tail into a false sense of security. Or they might try to confront them or make an escape. A common scenario is when one party is being tailed by another and given away like this.
- One Batman arc has Selina Kyle run for Mayor of Gotham. Worried mobsters hire Gunhawk to silence the cunning minx, and Gunhawk tries sniping at her from an adjacent building during a fundraiser. Selina notices the sniper's reflection in a champagne flute, and dives for cover in the nick of time.
- In the My Little Pony: Friendship Is Magic erotic fanfic Complicated Relations, there are two times when the same reflective surface reveals a character spying on two other characters having sex. And ironically enough, in both cases it's the same characters — Twilight, Cadance and Shining Armor — except with Twilight and Cadance's roles reversed in terms of who's spying on whom.
- Pocahontas: While John Smith is exploring Virginia, Pocahontas follows him out of curiosity, keeping out of sight. When he stops by a waterfall to get a drink, he notices her reflection and casually gets up then goes to ready an ambush.
- In Aladdin, Jasmine attempts to distract Jafar so Aladdin can grab Genie's Lamp, but Jafar ends up seeing Aladdin in the reflection on her tiara.
- In Mr. Bug Goes to Town, as Mr. Beetle goes over his Evil Plan with his hench-bugs, he polishes his top hat and sees an angry-looking Hoppity in its reflection, cluing him in that he overheard the whole thing.
- The opening of Goldfinger has James Bond making out with a sultry cabaret dancer and look longingly into her eyes... which reflect her accomplice coming up behind Bond to try delivering a crack to his skull. 'Shocking', indeed...
- The Man From Uncle has Solo at the customs station going into East Berlin when he notices a Russian following him in a camera flash reflector. Later that turns out to have been deliberate so the customs agent could slip a bug into his suitcase while he was distracted.
- Jurassic World: When in the gyrosphere, the kids are aware of the Indominus' presence a few seconds before it attacks by seeing its snout reflected on the window.
- Raiders of the Lost Ark. As Indy is driving the truck carrying the Lost Ark of the Covenant, he looks in his rear-view mirrors and sees German soldiers climbing along the outside of the truck toward the cab so they can attack him.
- In Transporter 2, Frank discovers a bomb has been planted on his Audi when he sees it reflected in a puddle.
- The Mexican: Jerry is changing a flat tire and sees, in the reflection of the hubcap, his supposed ally Leroy pull a gun on him. Leroy (actually Winston, hired to kill Jerry), not knowing he's been spotted, relents and goes to help with the tire. He then sees the reflection of Jerry pulling his own gun, who takes advantage of the opportunity and shoots Winston.
- Who Framed Roger Rabbit: While Eddie is "chatting" with R.K. Maroon, he notices a gun reflected in Maroon's office window and dives for cover just as it open fire. Maroon, however is caught out in the open, but he was the actual target anyway.
- Back to the Future Part II: While trying to get the almanac from Biff's car, Marty begins creeping up along the driver's side on his hoverboard, but Biff sees him in the side mirror and is ready when he gets close enough.
- Dead Presidents. The well-planned heist starts to become unraveled when the driver of the armoured car sees a robber in his rear view mirror and shouts a warning.
- Assassins. Bain is about to shoot Rath In the Back. If Rath turned to fire, he'd be killed before he got a shot off. So Electra puts on her sunglasses, enabling Rath to kill Bain by firing his gun Offhand Backhand.
- Firestorm (1998): When Karge is sneaking up on Jesse in the trading post, Jesse looks up in time to see Karge reflected in the shiny bell of the old-fashioned telephone he is using. He ducks in time to save his life, but Karge's swing destroys the phone.
- According to the local folklore of Hoxne, Suffolk, the town was the place where King Edmund of East Anglia was captured and tortured to death by Danish invaders. Supposedly the king hid under a bridge later called the Goldbrook Bridge while the Danes were searching the town, when a newly-wed couple who crossed the bridge saw the reflection of Edmund's golden spurs glinting in the water below, and promptly revealed him to the Danes. On the basis of this legend, local tradition considers it unlucky for wedding parties to cross Goldbrook Bridge.
- Feet of Clay: Vimes sees an assassin's attack coming in his shaving mirror in time to dodge. It's hinted that the mirror's design and placement have been carefully chosen to facilitate this.
- In The Mad King by Edgar Rice Burroughs, the hero is attacked from behind, but sees his attacker reflected in the glass over a framed picture. He then takes the picture off the wall and hits his attacker with it to buy time.
- The Specialist by Gayle Rivers. Two people are warned of a terrorist ambush when one of them sees a man pretending to look into a shop window, which reflects the submachine gun he's hiding under his coat.
- Babylon 5, episode "Revelations": After Garibaldi gets shot In the Back at the end of the first season, he has telepath Talia Winters come to jog his memory to see if he can remember who shot him. As he relives the incident, he notices a reflective surface where he sees his second, Jack.
- The "Eye Spy" episode of Agents of S.H.I.E.L.D. has Ward impersonating a woman with a camera eyeball monitored by the bad guys. He's fine until he accidentally passes in front of a mirror and the handler looking at the camera feed sees a white man in spectacles instead of a black woman.
- World of Warcraft: The end of the quest "The Tidestone: Shattered" has you staring at the reflective surface of the Tidestone core, seeing something on its surface, right before Athissa's naga capture you.