- Action Survivor: She's forced to become this to survive both the cave and the Crawlers.
- Ax-Crazy: Still suffering from the trauma of the car crash that took her family, Sarah becomes even more unhinged once the Crawlers attack.
- Break the Cutie: Starting with the death of her husband and child, and then the death of Beth.
- Final Girl: She's the last one alive, but the UK ending makes it clear she'll be dead soon.
- Go Mad from the Revelation: Although she's not the most mentally sound after the death of her family, she gets hit with a bad case of this after learning that Juno left Beth to die, and then it really sets in with the revelation that Juno and Paul were having an affair.
- Howl of Sorrow: She lets out a pretty magnificent one after killing Beth and fighting off numerous Crawlers.
- Not So Different: Of the He Who Fights Monsters variety. Her Howl of Sorrow is designed to sound like a Crawler shriek, and she eventually even moves like a Crawler.
- Sanity Slippage: Sarah seemingly didn't seek any psychiatric help to deal with the trauma of the car accident that killed her family; throughout the film she hallucinates, has terrible dreams and her mental state only grows worse from there on. Because of this, she makes the not-so-wise decision of picking Juno in the leg right after a huge fight against the crawlers. Apparently she can handle them all herself!
- Took a Level in Badass: Sarah was initially a rather meek, quiet woman still suffering from the trauma of her losing her family. Over the course of the film, she finds new ways to deal with that trauma by turning into a killing machine.
- Woman Scorned: There is a subtle wedge between her and Juno caused by their shared affections for Sarah's late husband.
- Accidental Murder: While fighting off Crawlers, she reacts without thinking and mortally wounds Beth on accident, eventually leading to Sarah having to Mercy Kill her.
- Action Girl: Rises quickly against the Crawler threat compared to the others.
- Foil: To Beth. Beth is Sarah's kind best friend who protected and supported her throughout her all-consuming grief over her husband and daughter. Juno is a selfish, impulsive adrenaline junkie who gets them all killed as a result of her recklessness.
- It's All About Me: Juno's biggest flaw is how self-obsessed she is, viewing others only in relation to her.
- Left for Dead: Her eventual fate; Sarah wounds her and abandons her to the Crawlers. She does wind up finding an opening, but, after she gets out, we don't see her again.
- The Mistress: For Sarah's husband, Paul.
- Ms. Fanservice: Not overt, but it's there. Natalie Mendoza certainly shows how flexible she is, and all the dirt somehow seems to emphasize her beauty. There's also some slight cleavage on display.
- Never My Fault: Refuses to accept responsibility for any of her major screw ups: her affair with Paul, lying to the group about what cave they were in, or her Accidental Murder of Beth.
- Spicy Latina: If she shares the same background as Natalie Mendoza, Juno has Spanish and Filipina ancestry, but she's also very Hot-Blooded.
- Token Minority: In a group full of white women, she's the only woman of color.
- Vasquez Always Dies: Although less of an example than Holly, who dies first, Juno is Left for Dead in the closing moments of the film by Sarah.
- What You Are in the Dark: She abandons Beth after mortally wounding her and hides her actions from her friends.
- Your Cheating Heart: She was The Mistress to Paul.
- Almost Dead Guy: Hangs on long enough to tell Sarah of Juno's actions despite her wounds.
- Better to Die than Be Killed: After being mortally wounded and dragged to the Crawlers' feeding ground, Beth begs Sarah to kill her rather than let her keep suffering in the dark.
- Big Sister Instinct: To Sarah, though they aren't actually sisters.
- Deadpan Snarker: Her responses to Juno are often witty remarks.
- Hot Teacher: At one point she notes that she's "an English teacher, not fucking Tomb Raider".
- Left for Dead: By Juno, who didn't anticipate that she'd live very long after taking a pick to the neck.
- Living Emotional Crutch: To Sarah after the death of her whole family.
- Mercy Kill: Given one by Sarah.
- Only Sane Man: Beth is the most sensible, level-headed and rational of the group.
- Team Mom: She's the one who reassures the group and makes sure they're doing everything safely.
- The Smart Guy: It comes with being a teacher. Beth's the one to figure out there's another exit to the tunnel by studying cave paintings.
- True Companions: With Sarah. Juno, Sarah's supposed best friend, abandoned her after the tragedy but Beth stood by Sarah and supported her the whole way through.
- Adorkable: Best examined when she puts on a pair of novelty glasses.
- Hair of Gold, Heart of Gold: Has blonde hair and is a very Kindly character.
- The Medic: Of the group; she's training to become a doctor.
- So Much for Stealth: Her gift watch goes off as she tries to hide from Crawlers, but luckily ditches it before she and Rebecca are found.
- Taking You with Me: After having her throat torn out, she manages to stab the Crawler that did it. Subverted, as it survives.
- Took a Level in Badass: A meek, sweet, and childish student doctor who fiercely manages to fight off and kill several of the Crawlers.
- Big Sister Instinct: To Sam, whom she loves dearly. Rebecca puts herself in danger and even considers abandoning the others to ensure Sam survives.
- Cruel and Unusual Death: She's utterly ripped open by a Crawler in the most graphically horrific death in the film.
- Freak Out!: She's most prone to doing this; after finding the Crawlers feeding ground, she starts screaming out for help even though logically there's no way anybody could hear her.
- Gutted Like a Fish: How she dies.
- Hysterical Woman: Rebecca is the most emotional character in the film, often exasperating the situation with emotional outbursts.
- Boyish Short Hair: As part of her tomboy nature.
- Jerkass: Holly is something of a loud-mouthed, tactless jerk, though the girls try to be patient with her.
- Miss Swears-a-lot: Holly rarely forgoes cursing when she speaks.
- Too Dumb to Live: Her recklessness and tendency to rush forward blindly costs Holly her leg, and ultimately her life.
- Reckless Sidekick: She loves climbing, but often ignores safety to Juno's frustration.
- Vasquez Always Dies Holly is the most tomboyish and reckless of the group, and ends up the first victim of the Crawlers.
- Wild Child: She's a hardcore 'sports fuck' who enjoys basejumping and the like.
A cave-dwelling off-shoot of humanity that feast on flesh.
- Ape Shall Never Kill Ape: As brutal as they are, the Crawlers seem to be fairly close-knit and are not seen harming each other. They even seem to grieve the deaths of their own.
- Big Bad: Of the entire film, they are the biggest threat.
- Fangs Are Evil: The first warning that they are savage creatures and are most certainly carnivorous.
- Human Subspecies: According to Word of God, they're cavemen who never left the caves and have since adapted to survive entirely in darkness.
- I'm a Humanitarian: While the Crawlers appear to mostly feed on animals, they're not fussy when it comes to feeding on humans. According to Neil Marshall, they are evolved cavemen, so they could technically be considered cannibals.
- Mama Bear: The first female Crawler seen in the film appears shortly after Sarah kills the Crawler's child. Upon learning that her child is dead (after a surprisingly sad moment of the Crawler desperately and pitifully nudging the body), she immediately goes berserk.
- Morlocks: Cannibalistic subhumans living underground.
- Non-Humans Lack Attributes: Genitals, nipples, etc. are not made visible on the Crawlers, though they are clearly capable of reproduction.
- Non-Malicious Monster: All things considered, the Crawlers are really just animals. Vicious and bloodthirsty animals, sure, but they're behaving just like any other animal would when a food source wanders into their territory and endangers their young.
- Tertiary Sexual Characteristics: Male Crawlers are bald while female Crawlers have hair.
- Wall Crawl: The first sign that they are something much scarier than any human. They are extremely agile climbers and can suspend themselves on ceilings with ease.