Predators develop senses that help them hunt. Sharp sight, delicate hearing, a keen nose... and Vein-O-Vision. Dracula and his ilk, as well as weirder fare, will have among their Super Senses the ability to see all the major and minor blood flows in a human body, often going to near X-Ray Vision levels by seeing their dinner's still beating heart!
This is something of a subconscious power, usually triggered by hunger. Vein-o-vision may be noticeable to onlookers if the character also manifests Animal Eyes or Glowing Eyes, but otherwise the power is inconspicuous. A Vampire Refugee or Friendly Neighborhood Vampire will probably have to use Heroic Resolve to resist sucking on so many delicious veins in plain view. As such, this can cause a Tomato in the Mirror or similar effect on a character once they realize their best friend is now on the dinner menu.
Also in a pinch, makes the stalking vampires' POV sequence all the creepier, showing us just how much of a Happy Meal the hero is to them.
This trope isn't restricted to the supernatural. As the page quote and picture show, it's also possible to make a technological equivalent of this trope for spies and soldiers. Typically it acts as a cross between X-Ray Vision and Infrared Xray Camera, allowing the agent using it to detect both the presence and Weak Points of enemies.
- The Chakra lines seen by the Byakugan in Naruto look like this. In addition, the technique itself makes its user's eyes rather ...veiny.
- In Vampire Hunter D, Meyer Link gets from time to time when he looks at Charlotte Elbourne, his human lover.
- In Vampire Knight, we see that Yuki, and thus probably all other vampires, can detect blood flows.
- Baki the Grappler's Hanma Yuujiro can see, or feel, or just perceive the flaws in everyone's body. So he is able to predict diseases and attack the weak points of any living being.
- Justice Society of America: Dr. Mid-Nite's altered vision—he cannot see on the light spectrum and is legally blind—is generally depicted as him being able to "see" the outline and heat of things,. He uses this to help him in his job as the premier surgeon for the DCU's superhero community as he can "see" what's going on inside his patients' bodies.
- In The Keys Stand Alone: The Soft World, John's water sense is so acute at short distances that he can sense people around him as constructs of water and know to the drop how much he can take from them without permanently harming them. Undoubtedly he can sense blood flowing in veins.
- Used in Night Watch as the main character watches a boy while a vampire.
- The not at all friendly vampires in Van Helsing have this power.
- Appears for a brief moment in Francis Ford Coppola's Bram Stoker's Dracula.
- This is how vampires see people in in Vampire Girl vs. Frankenstein Girl.
- The mad scientist in the film version of From Beyond, having acquired Horror Hunger after his peek into another dimension, has flashes of Brain-O-Vision, seeing through people's skulls to the gray matter he craves.
- Part of the fake, made-up, not-to-be-taken-for-real Karmic Twist Ending in Roald Dahl's The Wonderful Story of Henry Sugar.
- Howlers were mentioned as being able to see their enemies' "weak points", such as blood vessels, in Animorphs.
- Genevieve from the Warhammer novels has this ability.
- Salacia von Humperding in the Discworld novel Thud!:
"I can count fifty-seven hearts beating," said Sally.
Angua gave her a Look. "You know, that's one particular talent I'd keep to myself, if I were you."
- Actually all of the vampires on the Discworld have this ability. The only living things they CAN'T detect are any of the various species of the Troll family. (Or is it Genus?)
- Similarly, heart hounds in The Sword of Truth series hone in on the sound of their prey's heartbeat.
- Shows up in Anita Blake a lot, with a bit of synaesthesia (nothing supernatural is described in pure sensory terms). Anita tends to perceive the veins as leaping out of the skin, begging her to tear their owner's throat out and free them from their prison. (She's not actually a vampire, but...)
- The Monster of the Week in the Supernatural episode "Metamorphosis", a man whose transformation into a monster will be completed by his first bite of human flesh, experiences this after his wife cuts herself. He flees to avoid hurting her.
- Hungry vampires get this in Moonlight (2007). Mick, a Friendly Neighborhood Vampire, does this when trapped in a desert with the only human being around a pregnant girl.
- On Helix, a Vector crawling through an overhead air duct looks down at some people through a ceiling vent, and seen a web of green lines - either blood vessels or nerves, it's not clear which - threaded through a potential victim's body.
- In a non-supernatural variation, the autistic protagonist of The Good Doctor can map out a patient's cardiovascular system in his mind with only a glance.
- The Dungeons & Dragons third edition supplement Complete Scoundrel offers the spell "Healer's Vision," which is usable by two classes. Clerics who cast it can heal the target better because injuries become easier to see; Assassins can make use of it because being able to see your target's organs takes the guesswork out of where to stab them.
- Batman: Arkham Asylum and its sequel, Arkham City give Batman this in the form of "detective vision" built into his cowl. It acts as night/X-Ray Vision and gives him info on how alert/paranoid the Mooks are at any given moment.
- In The Witcher 2, Geralt can get Vein-O-Vision, as well as night vision, by drinking a Cat potion.
- One of Jericho's main powers in Dark Watch.
- In the Dead Space 2 multiplayer, Necromorph players get a variation where they see the nerves of human players, which change color based on the health of said human player.
- In The Darkness 2, the major arteries and veins in the chests of fallen enemies glow faintly to Jackie, while their hearts, which can be ripped out and eaten by the titular Darkness inhabiting Jackie, glow brightly.
- In Deer Hunter, noctovisor shows heart and lungs of animals.
- In Satellite Reign, the Support's World Scan ability lets you trace data and power lines to their source, letting you know which machines to hack or destroy in order to disable things like cameras or gates.
- Cole MacGrath in InFAMOUS:Festival of Blood can use his vampire sense to see everything in vein-o-vision. This helps him discern hidden vampires from normal humans as the latter apparently don't need a circulatory system.
- In Jurassic: The Hunted, you can exploit a dinosaur's weak-points by entering Bullet Time, which also reveals their internal organs.
- Truth in Television: Vampire bats have a limited thermographic sense, allowing them to select the best places to bite. They're not actually looking for veins to penetrate, but for areas where skin is thin enough to bleed easily. Given that such bats' usual prey (livestock or poultry) are thicker-skinned than humans, this is a handy sense to have.
- Mosquitoes also uses some sort of a thermal imaging to detect nearest vein to the skin, as do assassin bugs.
- Various "vein viewer" or "vein vision" devices, largely based on principles of transillumination, claim to allow medical providers to "see" deep peripheral veins for intravenous access. This can be a handy trick in an emergency, or if you need an IV on someone with poor surface veins. Unfortunately the devices rarely work as advertised - a skilled phlebotomist can do just as well or better without the device, and the devices occasionally fail to visualize surface veins that can easily be seen with a naked eye.
- Angiograms are used before many surgical procedures to plot the precise locations of blood vessels before an operation.
- Pulse oximeters evaluate a person's oxygen saturation by passing paired beams of light through the subject's fingertip to a photodetector, then calculating how much light from each beam - one the color of oxygenated blood, the other lacking that hue - was blocked in transit. In effect, they work by Artery-O-Vision.