So what prevents a predator from plunging down the hobbit hole after a wombat? Oh, only one of the most formidable fannies in the animal kingdom.

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“A wombat’s rump is very tough,” says Alyce Swinbourne, a PhD candidate at the University of Queensland. “Their dermal shield is essentially four fused back bones or plates covered in cartilage, fat, thick skin, and fur.”

Swinbourne is a bit of an expert on wombat backsides, by the way. In 2014, she developed a method for retrieving uncontaminated wombat urine so she could test it for hormone concentrations. In lieu of invasive methods such as a catheter, Swinbourne taught the wombats to tinkle each morning when she tickled their tushies.

Swinbourne got the idea for tickle induced tinkling by watching female wombats with their young. Like many marsupials, mothers lick the cloacas of small wombats to get them to pee. Swinbourne replicated that maternal action with a light tickle. “The reward for urinating on demand was a firm rump scratch," she says.

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It would have to be a pretty firm scratch for the wombat to feel it. All of that gristle is the wombat’s primary defense against dingoes and other predators. The wombat simply dives into its burrow and plugs up the end with its caboose. The predator can claw and bite at the wombat’s backside all it wants, but those buns of steel protect it from any significant harm.

There’s even evidence that a wombat dermal shield can be used as an offensive weapon, a la Captain America. It’s thought that when a predator becomes too persistent, the wombat can slam its butt against the roof or walls of the burrow and literally crush the skull of its enemy.

“I have seen dead foxes near the entrances to burrows,” says Michael Swinbourne, a PhD candidate at the University of Adelaide.

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(Yes, Alyse and Michael are married. She tends to be more interested in wombat biology, particularly reproduction, while he researches wombat population ecology. You know what they say – the couple that studies wombats together stays together.)

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“Wombats also have very large and very sharp claws for digging through hard ground, and very sharp teeth,” says Michael. “I have seen what these can do to zookeepers, and it is not pretty.”

The wombat has a few other adaptations that make life below ground more comfortable, such as a tolerance for low oxygen levels and a backward-facing pouch controlled by a sphincter. The latter is thought to prevent wombat joeys from growing up with a mouthful of dirt, but Michael points out this is only speculation. Koalas also have backward-facing pouches, and they live in trees.

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Even above ground, you probably don’t want to tango with a wombat. An Australian woman was mauled by one in August, resulting in 20 bites and lacerations, some of which required stitches. It took two other adult humans to disengage the marsupial, and the woman was quoted as saying she thought she was going to die.

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This isn’t to say all wombats are hole-dwelling death-eaters. In fact, between Michael’s work raising orphaned joeys and Alyce’s work with captive wombats at the Australian Animals Care and Education wombat breeding facility—are these guys a power couple or what?—the Swinbournes say the stocky marsupials can be quite cute, almost like the family dog.

Besides, you can’t fault an animal for evolving adaptations that enable it survive, even if one of those adaptations is a lethal keister. It’s even possible that the armored butt first evolved as a way to protect wombats not from predators, but from each other.

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“Mating appears to be a means of wearing the female down,” says Alyse, “a test of fitness for the male. If he can overpower her, he can mate with her. This can be very taxing on the male if the female is strong and has a dominant personality.”

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And if that dominant female decides to fight back with her deadly derriere, her would-be mate doesn't stand a chance.

Jason Bittel writes about weird animals for a living. You can find more of his work at his website.