Double Tap

"Somebody comes through that door, you give him two in the chest and one in the head."

—Captain Mike Steele, Black Hawk Down

An amateur only shoots once. A professional always shoots twice. A subtrope of Boom! Headshot!, this is the difference between a sniper and a more up close and personal silenced pistol assassin. Better safe than sorry, after all. The Double Tap seems like overkill, but it's actually pragmatism at its finest. [['Tis Only a Bullet in the Brain|People surviving a headshot are rare, but they happen, and there's nothing like someone surviving a headshot to ruin your carefully laid plans. However, two to the head is much more likely to be certain. Some training methods insist on at least one shot to the torso and two to the head (still not overkill, really: even if you survived two shots to the head, a fatal shot to the heart means that you now have two life-threatening injuries to recover from, and most people die from either one), but two to the head tend to be just as effective...usually.

Compare and contrast Coup De Grace, which also serves to confirm a kill but is usually viewed negatively due to being delivered to already disabled or downed foes.

Examples :

Anime and Manga

Batou double taps a surprised Special Forces fighter near the end of Ghost in the Shell: Stand Alone Complex.
In Change 123, Fujiko was trained by her father to shoot every target twice; once in the head and once in the heart.
Referenced by name and perforned by Gun nut Kohta Hirano in Highschool of the Dead. He doesn't even wait for the first bullet to finish its faithful journey before firing the second.
When Vanessa learns to shoot in Madlax, the eponymous heroine explains that double-tapping is more efficient than single shots.
Specifically emphasized by Tenma's trainer in Monster.

Film

Zombieland has this as Rule #2 for surviving the Zombie Apocalypse. Despite the zombies in the movie being of the Technically Living variety, the characters frequently make sure to Remove The Head Or Destroy The Brain. This is seen performed with guns, giant mallets, and even a car at one point.
Near the beginning of Beverly Hills Cop Mikey Tandino is executed by two shots in the back of the head. Axel Foley's captain notes that it was a professional hit.
The Godfather: When Michael goes to kill Solozzo and his bodyguard McCluskey at a meeting, Sonny instructs him "Two shots in the head apiece."
There's a Hong Kong action movie named Double Tap, about a series of murders where the victim always had two bullet holes in the head, close enough to form an '8'.
John Wick, being an experienced assassin, usually shoots his foes at least twice and in the head.
In The Raid, Jaka shoots a mook he's wrestling with thrice in the head.

Literature

Murphy mentions (and does) this several times over the course of The Dresden Files.
In the book 'Vengeance' (the basis for the film Munich), the author recounts his shooting lessons during Mossad training. The instructor told the class to always fire two shots at a time. "Always BANG BANG...Never just god-damned BANG!"
John Kelly of Tom Clancy's Jack Ryan series uses this technique extensively in Without Remorse, largely because of his SOG/SEAL training, with his Colt .45. When he configures it as a .22 with a home-built suppressor, his especial reliance on the double-tap headshot is mentioned as particularly necessary given the .22's relative weakness—and as an indicator to the investigating policemen that they're dealing with an experienced professional. When he switches it over to .45 configuration, he changes to two in the chest, one in the head, a sign that he's discarding subtlety for the last push.
In Artemis Fowl, Butler's preferred technique is two to the chest, three between the eyes.

Live Action TV

The Mozambique Drill (see Real Life) has also been used in Dexter.

Video Games

In Borderlands fourth DLC, the Claptrap Ninja Assassin does this to the arms merchant just before the final boss battle. Also, the Jacob's brand of weapons (which have the highest damage) uses the lack of this as their selling point; "If it took more than one shot, you weren't using a Jacobs".
Mass Effect 1:
- If Wrex dies on Virmire, his killer ( either Shepard or Ashley) will shoot him three times when he's already on the ground. This is a pretty good practice with krogan enemies in regular gameplay, too.
- At the end, Shepard tells his / her companions to check if Saren is really, absolutely dead after he has already either shot himself in the head as a heroic sacrifice or been impaled through the chest. One of them will give the body another shot to the head. But anyone being slightly Genre Savvy knows right away that if the developers added that scene, the body will get up again.
In the opening level of Mass Effect 3, Liara suspends a few Cerberus troopers in the air with Singularity, shoots them, then puts a few more rounds in them when they're on the ground.
The protagonist of Fallout: New Vegas gets doubletapped at the beginning of the game - and survives.
In Call of Duty: Black Ops zombie mode there is the Double Tap Root Beer item, which causes every pull of the trigger to fire two rounds, even when using pump action shotguns or bolt action rifles. While doubling your rate of fire sounds fun, scarcity of ammo can to push this into Awesome but Impractical.
A Sniper with the "Croc-O-Style" item set in Team Fortress 2 will not be killed by headshots and thus will require a double-tap to kill.
- A Spy wielding the Ambassador can kill weaker classes in as few as 2 shots.
In Thwaite, the best option when dealing with a balloon or MIRV that just split into three missiles is to destroy two with one of your missiles and the third with another.
In Wolfenstein: The New Order, one of the stealth kill animations involves stabbing a mook in the head twice.

Western Animation

Jonny Quest episode "A Small Matter of Pygmies". After downing a black leopard, Race Bannon shoots it again to make sure it's dead.

Real Life

There's the Mozambique Drill, which is a double tap to the chest followed by an aimed shot at the head.
British Special forces are taught to double-tap the head, if possible in the "T" (a line from temple to temple, then down the nose), because body armour has become an awful lot easier to get hold of nowadays.
Osama Bin Laden reportedly took one to the chest, one to the eye.
Somewhat averted in that many firearms instructors now teach students to shoot until the threat is neutralized, regardless of how many rounds that is, so some people now shoot triple taps or just punch out five or six rounds rapidly per target.
Standard police training in most American districts is that if you are in a situation where you're actually shooting at someone, you always pull the trigger twice.