Isaac: Shit! I fuckin' hate these zom—The House of the Dead: OVERKILL is a prequel to the original House of the Dead series. It takes the unintentionally bad voice-acting the series is known for and runs with it, resulting in an over the top 1980 B-Movie vibe; heavily inspired by Quentin Tarantino's Grindhouse.The plot of the game follows Agent G and reluctant partner Detective Isaac Washington. They're hunting down the deranged crime lord/pimp, Papa Caesar, fighting through the waves and waves of mutants he's unleashed. While they're tracking down Caesar, he causes the death of Varla Guns' brother, leading the hottest stripper on the Bayou City club scene to track down Caesar herself to take her revenge. She'll have to get in line though; as Washington wants to get revenge for the death of this father, also caused by Caesar.Initially released exclusivity on the Wii in 2009, an Updated Re-release, the Extended Cut, was later released for the PlayStation 3 with PlayStation Move support in 2011. The Extended Cut features sharply improved graphics, new bonus weapons, and two levels not seen in the original Wii version, "Naked Terror" and "Creeping Flesh", which focus on Varla Guns' story.A PC port of the Extended Cut followed just in time for Halloween 2013, as The Typing of the Dead: Overkill (which includes the stand alone game) which is a follow up to the Cult Classic The Typing of the Dead released on the Dreamcast and PC as well as Japan-only The Typing of the Dead 2 for PC. This version also offered several purchasable dictionary DLCs which change the words needed to type with William Shakespeare, Filth and Love based dictionaries available. In addition House of the Dead: Overkill - The Lost Reels was released for iOS and Android devices on April 25, 2013.
G: Mutants. How many times do I have to tell you to not use the Z word?
G: Mutants. How many times do I have to tell you to not use the Z word?
They've come for tropes. You'll give them...examples:
- Achilles' Heel: All bosses have one pointed out just before you enter the fight.
- Action Commands: In the Extended Cut, represented by "dunk tank" targets that pop up onscreen to either let you fight off a close-up attacker or avoid a highly damaging attack.
- Action Girl: Varla Guns; heavily lampshaded in her introduction voiceover. She slowly turns out to be a Faux Action Girl, though, which is itself lampshaded too, but the Extended Cut, in turn, defies that status by putting her and new character Candi Stryper in the spotlight, via the all-new exclusive Naked Terror and Creeping Flesh episodes.
- Added Alliterative Appeal: The steam achievements for Typing are pretty much nothing but these including: Painful Punctuation, Lascivious Lexicon, Critical Clause, Grotesque Grammar, etc. The default phrases you have to type at Coco in "Naked Terror" are also alliterative.
- An Arm and a Leg: Candi's right arm gets chopped off by the boss's giant axe/cleaver when it falls from a steel beam above them. She dies from the blood loss.
- Awesome, but Impractical: The Minigun. No need to explain why it's awesome, but its cool-down period is rather long if you allow it to overheat, leaving you a sitting duck for a good three or four seconds— which is an eternity in games like this. Restricting it to short bursts can help avoid the problem, but that kind of defeats the purpose of the Minigun to start with, and is a totally unviable strategy in the final boss battle, where you're forced to use it.
- The regular ol' Shotgun is very cool in that old-school "shk-shk-BOOM" sort of way, but reload times are the main Achilles' Heel with your guns, and each shell has to be loaded into this gun one at a time. What's more, the presence of the Auto-Shotgun makes it practically obsolete right out the gate.
- Appendage Assimilation: Nigel and Sebastian.
- Artifact Title: Subverted in a metaphorical sense. A good deal of the levels take place in "houses", i.e. the fun house, the big house, the whore house...plus, the presentation is very grindhouse-inspired.
- Ascended Meme: Suffer Like G Did is both Agent G's theme song and a PS3 trophy. note
- Awesomeness Meter: Goregasm!
- BFG: Issac and G use miniguns during the final boss fight. How they got access to them becomes a Noodle Incident, as the first part of the boss fight simply shows "missing reel", and when the "movie" resumes, they're standing victorious with the miniguns.
- The Big Easy: The setting is around a theme park version of New Orleans called "Bayou City" (the issue is muddied by a few characters mentioning the "county" they're in, but that's exactly the kind of mistake a real grindhouse B-movie would make* ).
- Bittersweet Ending: G and Issac stop Papa Cesar and Clement from unleashing their plans, but Varla's brain ends up getting separated from her body, and they can't undo that because the last boss fight was against the mutated form of it. To make matters worse, the audio tape Caesar sent G and Issac reveals his true motive: to inform them of the underground facility of Clement's and the powerful men pulling the strings behind (Curien and Goldman). Granted, Issac is very likely to be unaware of this until it is too late. Plus, his father is stated to be still alive.
- Blaxploitation Parody: Isaac Washington is basically a straight sendup of the average blaxploitation hero, who uses "motherfucker" like most of us would use a comma.
- Body Horror: Many of the enemies, especially Nigel and Sebastian (two twins horribly fused together) and the Lobber from Overkill. And from the same game, Varla Guns, after Warden Darling put his mother's brain in her head... and apparently forgot to reattach the back of her cranium. Extended Cut adds the Dual Boss Sindy & Coco, respectively a Distaff Counterpart to the above Lobber in the looks department and a mutant monkey stripper.
- Boom, Headshot: The best way to kill the mutants.
- Bond One-Liner: Washington is the king of these.
- Brain in a Jar: At the end Varla Guns is nothing but this.
- Bragging Rights Reward: The Gwendolyn, from the PS3 Extended Cut. Easily the best gun in the game by a wide margin, but by the time you obtain it you've already beaten the game twice to unlock it (the second time using only the basic AMS Magnum) and then beaten several more stages to farm enough money to buy it.
- Brick Joke: Washington calls G "Agent Gwendolyn" at the beginning of the "Carny" chapter; G doesn't protest until two chapters later after being kicked awake.
- Camping a Crapper: Agent G makes a discovery that mutants use the toilet like normal people and mentions it'll go in his report as a "potential weakness". Washington is less than impressed.
- Circus of Fear: The aptly named Carny level.
- Cluster F-Bomb: Someone personally counted 370 of them. And that's not everything yet!
- Lampshaded in the last level:G: Care to dial down the swearing, Wash?
Isaac: Fuck that, motherfucker!
- G lampshades again when he notices that, of all the things they saw, the only thing Washington didn't call a "motherfucker" was Warden Darling, who actually was a literal mother fucker.
- The PS3 version of the Extended Cut plays with this: the speech is censored by default, in both voice and subtitles. How do you restore the dialogue to its foulmouthed glory? By shooting the censored words during cutscenes.
- Lampshaded in the last level:
- Comically Missing the Point: the Carnival level has one:G: (Sees an explosion in the distance) This is bad.
Isaac: Damn right, this is bad! You've seen the prices?!
- Contemplate Our Navels: The end has the characters discuss the true meaning of their ordeal, with Washington thinking it's a postmodernist deconstruction of modern feminism. And swear gratuitously... even G, though he's just mocking Washington.
- Continuity Nod: The version of G's theme tune that plays over the main menu is titled Suffer Like G Did.
- Critical Existence Failure: No character will even comment on being hit so if you're not paying attention to your health meter it can be surprising to see the game over screen.
- The exception is in the Extended Cut version of the first boss battle, where Washington will comment on how disgusting it is to be hit by a flying arm or what have you.
- Cowboy Cop: Isaac Washington would probably be this if we saw him do police work instead of shooting mutants.
- Damsel in Distress: Despite being able to handle herself fine in the Extended Cut levels, Varla Guns gets kidnapped twice afterwards.
- Dead Man Switch: The Warden has one at the end.
- Dead Weight: In the first few stages fat zombies are the earliest kind of Giant Mook, taking a few more body shots than normal enemies. The manual explains that a mutant's health is directly proportionate to its mass. They're also fast.
- Deconstruction: A parody of zombie movies in general. For example, in the ending, G and Isaac wonder what the underlying metaphor of this game was, with G suggesting "love isn't always right" and Isaac calling it a "damning indictment of contemporary feminism", pointing out that there are few other interpretations to "two dick-wielding cop cliches" taking down a "hundred-foot birthing mother". For another, during The Fetid Waters, Isaac asks G why they're immune to whatever it is that's creating all the mutants and nobody else is. They aren't; the compound has a short lifespan and, as they weren't exposed to the initial dosing, they simply haven't been infected - G because he only got into town afterward, Isaac because he was at his mom's.
- Disposable Woman: Varla Guns. The trope is lampshaded and discussed by G at the end of the game.
- The Dog Bites Back: Jasper, forced to work with Caesar when Varla, who raised him, is threatened, eventually declares that no one threatens his sister and injects himself with a serum that turns him into the first boss of the game.
- Double Unlock: You don't unlock special weapons straight away; you instead unlock the option to buy them.
- Dropped a Bridge on Him: Papa Caesar is killed in the electric chair by Warden Darling, cheating Isaac out of his revenge. Candi also gets this in the PS3 version when a giant cleaver the boss was using drops from the rafters it had got caught on and slices off her arm. She winds up dying from blood loss.
- Dual Boss: Extended Cut adds a dual boss in the first new chapter, but one of the two mutants in question is so massive that it literally can't do anything except send a Shockwave Stomp or two at you, leaving you to deal with the smaller one for the whole fight.
- The incoming behemoths at the end of "Jailhouse Judgement" look to be this... and then they turn on each other, leaving only one (Brutus) to fight you.
- Dude, Not Funny!: Invoked: Isaac has one of these against Agent G's joke that he makes if you fail to save a survivor at the Carnival level.G: I guess he ordered ketchup with that.
Isaac: Tasteful, agent.
- Dumb Blonde: Candi, the second player who accompanies Varla in Overkill - Extended Cut.
- Early-Bird Cameo: The second of two chapters added to the Extended Cut "Creeping Flesh", lets you catch a quick glimpse of "Scream Train"'s boss, the Crawler.
- Every Car Is a Pinto: Exaggerated at the end of the first chapter:G: Tasteful ride.
Isaac: Don't disrespect my wheels! She's my pride and joy.
(Isaac's pride and joy promptly explodes for absolutely no reason)
G: (beat) Mm, we'll take my car.*
- Even Bad Men Love Their Mamas: Although in this case it would have been kinder to the audience not to show that kind of love.
- Fan Disservice: Plenty to go around in the Naked Terror level (exclusive to the "Extended Cut" edition) with all the zomb.. ehhh... mutant strippers. Specially the boss.
- Fanservice: The opening credits play over a live-action pole dance which has nothing to do with anything, possibly as an homage to Planet Terror.
- Faux Action Girl: Before the extended cut Varla's only screen time was basically driving around and being held hostage.
- Fire-Forged Friends: Overkill begins with Isaac sucker-punching G. Later in the game, after multiple others have asked G to just answer the damn question, Isaac crows "the 'G' stands for 'genocide', motherfucker!" after the two mow down another wave of mutants during one point in "Jailhouse Judgment". Isn't that sweet?
- Gatling Good: You get these for the final boss. How you found them, the game intentionally does not show. The gameplay change is represented in Typing of the Dead: Overkill by letting you mash on the keyboard.
- Giant Space Flea from Nowhere: The Crawler boss is almost literally this with the only explanation being that the mutagen doesn't only affect humans.
- Alternatively, given its additional human anatomy (human-like skin, a ribcage, feet with five toes, etc.) it is a severely mutated human, much like Meat Katie.
- Game-Breaking Bug: An irritating one; in the Crawler boss fight, wherein the circle highlighting the boss's weak spot is marked too high on its arm, and trying to shoot there won't do anything. Shooting it in the same spot it said to on the other side will cancel its attack and deal damage.
- The "Carny" chapter in the Wii version is very glitchy compared to the rest of the game. Its boss fight in particular is difficult to get through without the game freezing for whatever reason.
- The "Extra Mutants" mode appears to be an afterthought, as the added enemies tend to spawn in inconvenient locations. In one scene in "Ballistic Trauma" where hospital doors blow open and zombies swarm out, one female zombie only present on Extra Mutants can get stuck behind one of the doors. You can't kill her, and the scene won't advance until all on-screen enemies are dead. Unwinnable by Mistake ensues. On very rare occasions, the game will also forget you're in cutscene mode and have enemies attack you while you're unable to fight back.
- Gory Deadly Overkill Title of Fatal Death: The game's title is already an example by itself. In game the levels are a deliberate send-up of its parent franchise by means of turning it into a seventies exploitation film, with level subtitles such as "Papa's Palace of Pain" and "Jailhouse Judgment".
- Gosh Dang It to Heck!: Candi's momma taught her that if she can't say anything nice, then say nothing. Candi took that literally, and so actually uses the word "nothing" in place of swears.
- Grievous Harm with a Body: Jasper, Meat Katie and Nigel & Sebastian all hurl severed body parts at you as a means of attack. Nigel and Sebastian go the extra mile by throwing mutilated clown torsos.
- Groin Attack: Overkill being the kind of game it is, its manual takes the time to mention that this does not work any better than any other non-headshot.
- Played straight with the Screamer, though. Look closely at the weak-point markers.
- A well-timed kick to the 'nads can also be used against the burly convict mutants.
- Guns Akimbo: Isaac in has a habit of dual wielding his AMS Magnums, and it's actually a requirement that you dual-wield Wiimotes for some gallery achievements.
- Hate at First Sight: G and Issac Washington meet this way before they get better.
- Hide Your Children: Averted. The "Greg" enemies are obviously diaper-clad mutant babies.
- Hong Kong Dub: As a parody element, it pops up in several cutscenes, but especially noticeable in this one.
- Idiosyncratic Difficulty Levels: Bitch [easy], Agent [normal], and Motherfucker [hard].
- Instant Mystery, Just Delete Scene: Wearing its inspiration from Grindhouse on its sleeve, Overkill a similar sequence near the end, where Isaac Washington and Agent G both solemnly prepare to do battle with the Final Boss... then one MISSING REEL later, the two of them are standing outside the burning laboratory, remarking how convenient it was they just happened to find those gatling guns. Then they fight the Final Boss for real. (The "Director's Cut" verion later adds the supposed missing sequence back in.)
- Infinity+1 Gun: In the Extended Cut remake of Overkill, it's Isaac's favorite guns, the Gwendolyn. It has the power of the automatic shotgun, the range of the handgun, and it has Bottomless Magazines. Slightly mitigated by the fact that it doesn't have the crowd control of the shotgun, but why would you need it anyway? To get it, one must clear each stage (in any order) on Director's Cut once in "Classic Mode," where you're only allowed to use the default AMS Magnum.
- It's Personal: Papa Caesar killed Washington's father and indirectly killed Jasper. Then, Varla has to watch Candi bleed to death, making it extra personal for her.
- Jerk with a Heart of Gold: Isaac is crude, standoffish, extremely foul-mouthed and generally shows little in the way of tact or couth. That said, he acts annoyed at but ultimately doesn't correct G's assertion that, deep down, he actually likes G. Isaac also accidentally reveals that he avoided the mutant outbreak because he was visiting his mother.
- Kick the Dog: Papa Caesar is introduced as a bastard from the beginning, but the way he treats Jasper (who is almost totally paralyzed) is downright assholish. He calls him an "impotent cripple", whacks him in the face with his cane and warns him that continuing to insult him will jeopardize his sister Varla's safety before calling him a "fucking cabbage."
- Kill the Cutie: Aw, poor Candi. How very mother-nothing sad.
- Lampshade Hanging: In the last scene the characters pick apart almost every single trope that was used in the game (and the Exploitation Film genre), including Washington's excessive cursing and the fact that the only (decent) female character has absolutely no impact on the plot and ends up as a brain in a jar).
- Large Ham: The Narrator:Narrator: GGGOOOOREEGAAAAASMM!!
- EVERYBODY, with the possible exception of G. But then, keeping in line with the "B-Movie" presentation of Overkill, the joke is that he's a poor 'actor'.
- Lemony Narrator: The narrator again.
- Lighter and Softer: Reconstructed. While it's still no-holds-barred when it comes to the scenes of death and destruction and good ol' zombie Gorn, the dialogue, full of Isaac's potty mouth and G's Straight Man tendencies, helps lighten the mood a lot.
- Locomotive Level: "Scream Train", possibly a shout out to Resident Evil 0.
- Loves the Sound of Screaming: Papa Caesar.
- Ludicrous Gibs: Intentionally taken to ridiculous extremes.
- Make Me Wanna Shout: The Screamer, of course.
- Male Gaze: The camera lingered at Varla Gunns' cleavage before going back up to her face at the end of "Ballistic Trauma". Not to mention the live-action pole dance featured over the opening credits.
- The Man Behind the Man: Warden Darling for Papa Caesar.
- Mercy Kill: Jasper. Lampshaded through the entire scene in question, of course.G: I can help ease the pain.
Washington: No you can fuckin' NOT! Shoot the motherfucker!
G: Don't you do tact? That's what I am going to fucking do! Y'know-
Washington: Shut the fuck up and shoot! Shit!
(G shoots Jasper twice in the head)
G: Happy now, fuckwit?
- More Dakka: The machine pistol is one of the cheaper alternate weapons. With enough cash, you can also spring for the more powerful assault rifle. And for the final boss, you get the minigun, after which you can bring it along to the rest of the game with some serious cash.
- Multi-Armed and Dangerous: Nigel and Sebastian, by virtue of two people being conjoined together. Washington even yells for them to put all their arms up. Ultimately, though, Sebastian's extra arms don't factor much into the fight; he's simply Nigel's weak point.
- No Celebrities Were Harmed: Isaac Washington is, for all intents and purposes, an Expy of Samuel L. Jackson.
- Noodle Incident: The first phase of the final boss fight, which is skipped over in an alleged "missing reel". The dialogue immediately afterwards suggests that it would have been awesome.
- Subverted in the Director's Cut mode of the Extended Cut, where they reveal that they did find the miniguns and fought Mother by destroying pillars.
- Not Using the "Z" Word:Isaac: Shit! I fuckin' hate these zom—
G: Mutants. How many times do I have to tell you to not use the Z word?
- Number of the Beast: The end of the train level shows that the train's locomotive has has the number 666 on it.
- One-Letter Name: Agent G.
- "You ever gonna tell anyone what the fuckin' G stands for?" "...No."
- Isaac walks right through that open door when he once calls his partner "Agent Gwendolyn" in the intro movie to "Carny", and later on in "Jailhouse Judgement, he is quoted as saying "The G stands for 'Genocide', Motherfucker!".
- Packaged as Other Medium: It has a cover meant to look like a movie poster. The whole game is presented as a movie, with each level having its own poster (complete with credits) and a "missing reel" in the final boss fight.
- Parental Incest: Warden Darling almost definitely had this relationship with his mother, transplanting her brain into the body of Varla Gunns and making out with her. In the end, after the main characters kill the giant mutant version of his mother, he insists on returning to the womb in order to undo his wrongs. Agent G then notes the irony of Washington referring to everyone and everything as "motherfucker" except for Darling, which he translates into Washington not meaning anything he says, and therefore actually liking G as a friend.
- Postmodernism: In the ending of Overkill, the characters discuss the symbolism of their adventure, a Mythology Gag regarding the fact that zombie media often has some sort of symbolism regarding culture, politics, or some such.
- Promotion to Parent: Varla raised Jasper after their parents died.
- Rare Guns: The assault rifle is modeled after the XM8, despite the game being set in 1991. The standard AMS Magnum is also based on the Desert Eagle.
- Relax-o-Vision: The missing reel gag.
- Revolvers Are Just Better: You can buy a Hand Cannon that comes with its Firepower maxed out, which equates to everything that isn't a boss dying in one shot. A tad subverted - you need to be really fucking accurate with it, and you have to carefully time your reloads during down time because they take very long. The automatic shotgun is better at chaining combos and ammo capacity.
- Roaring Rampage of Revenge: This trope is invoked word-for-word by the narrator. Varla tries to go on one... but miserably fails. Twice.
- Sequel Difficulty Drop: Largely due to the ability to upgrade and switch weapons.
- Sequel Hook: The ending establishes that, at the very least, Bayou is not even close to mutant-free. And the poster for the last level says "They're just getting started."
- Justified Trope, at least in a strict chronological sense, it is a prequel.
- Not only that, there's the tape which Caesar leaves to Washington:Caesar: You know of Clement Darling, yes, the cretin prison warden? It was he who originally discovered the mutant compound in a secret lab beneath his prison. Clement's ambitions are small minded, Isaac. But he has friends, powerful friends. (Curien and Goldman, if you haven't guessed it yet.)
- Shout-Out: The whole game is one long one to grindhouse films (especially Planet Terror).
- There's also one bit where you fight through a zombie-infested train and fight a giant insect as a boss.
- "We're on an express elevator to Hell, going-" "Shut up and press the button!"
- One of the ranks for making consecutive kills without missing is "Ultra-Violence".
- "Suffer Like G Did" is also a quote spoken by Zeal (of the Judgement boss) in The House of the Dead 2.
- The boss "Screamer" (and associated color and sound effects) resembles female J-horror monsters like the one from The Ring.
- So many of the phrases in The Typing of the Dead: Overkill are references. For instance, you might have to type "Main screen turn on," "Make your time," or "Move ZIG" or "Looking for sailors", or come across a pair of zombies with "Careful now" and "Down with this", or "Fork Handles" and "Four Candles".
- Sir Swears-a-Lot: Isaac Washington, saying "fuck" in nearly every sentence.
- Sophisticated as Hell: After Cluster F Bombing his way into the Guinness Book of World Records, Washington manages this in Overkill's ending:Washington: Frankly, Casanova, I'd be more worried about reading the last 24 hours as a damning fucking indictment of contemporary feminism.
G: ...Beg pardon?
Washington: I just think two dick-wielding cop cliches taking down a hundred-foot birthing mother is a statement fairly limited in its interpretations.
- The Stinger: The game ends its credits by playing the tape Caesar left for the protagonists at the beginning of The Fetid Waters, which reveals that "powerful friends" (presumably Curien and Goldman) have access to Clement's compound, and more surprisingly, that Washington's father isn't actually dead...
- Sunglasses at Night: Agent G has his on throughout the whole game.
- Stylistic Suck: The game mocks the previous games' bad acting, running with it and turning it into a grindhouse film.
- Tattooed Crook: Varla has a red, lipstick-kiss tattoo on her left breast.
- This Is the Final Battle: Washington states that it seems like "this is it" as Mother prepares to attack them. G likewise gets sentimental with him for a bit before they both take aim... MISSING REEL
- Although the "missing reel" is seen in the Director's Cut.
- Title Drop: The last chapter in Overkill is appropriately titled "Overkill", with its intro detailing "Operation: Overkill".
- Title of the Dead
- Tragic Monster: Well, almost every single monster in the game was an innocent civilian before they turned into mutants. Two stand out, though: Jasper, per Transformation Trauma, and the Screamer, who's an unfortunate test subject used in Papa Caesar's experiments.
- Transformation Trauma: Jasper turns himself into the first boss by injecting himself with the virus. Given that he starts the game as a quadriplegic, his status as a boss is justified by his new Psychic Powers.
- 20 Minutes into the Past: Takes place in 1991 and was released in 2009.
- What Does He See in Her?: Varla explicitly asks Candi why Jasper went with her. Candi starts to explain, though Varla tells her to shut up.
- The Unfought: Papa Caesar and Warden Darling.
- Updated Re-release: Two of them: first, Extended Cut for the PS3, then Typing for PC.
- Vasquez Always Dies: Or, in this case, Varla Guns Has Her Brain Replaced With an Old Woman's and Her Body Mutated into a Horrible Monstrosity. Ironically, this traditional "Tomboy of the Tomboy and Girly Girl pair dies" part of the trope is inverted in Varla's exclusive chapters of the PS3/PC version of Overkill, which end with Girly Girl Candi getting her arm cut off by Meat Katie's blade, and bleeding to death. Considering this is set just before Varla devolving into a Faux Action Girl, this raises the implication that she underwent a Heroic B.S.O.D., and couldn't get out of it for the rest of the game.
- Was Once a Man: In addition to the usual zombies, Meat Katie's name tag and parts of the Crawler's anatomy suggest that they were human at one point. Varla also suggests Sindy and Coco were once acquaintances of hers before they were mutated.
- Why Did It Have to Be Snakes?: For Washington, why did it have to be elevators?
- Why Don't You Just Shoot Him?: Averted. As soon as Clement reveals himself as the Big Bad, Isaac Washington immediately takes aim and shoots... only to discover that there's a pane of bulletproof glass between them.
- Played straight at the start of Scream Train when all three protagonists have Caesar right where they want him, but their arguing over who gets to kill/arrest him allows him to get away. It goes on for minutes, before any of them notices. Even better, Isaac actually shoots Caesar while he's monologuing, and then promptly apologizes and asks him to continue.
- Ye Olde Nuclear Silo: Where the mutagen originally came from.
- You Killed My Father: Papa Caesar killed Washington's father.
- Zombie Puke Attack: Some zombies puke acid, with Not Using the "Z" Word explaining this as a genetic mutation in the victims.
Caesar: As you well know, Isaac, I enjoy TV Tropes. It's like a good Chinese dinner, you know, with the sweet and the sour. Expanding on that analogy, I will smile with delight—that's the sweet—as it ruins your fucking life—that's the sour. Ciao!