Looks can be deceiving, especially in the animal kingdom. These 6 cuddly animals may look adorable, but don’t get too close: they can be deadly.

1. Koalas

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Koalas mostly keep to themselves and spend 22 hours a day sleeping, but sometimes they can snap and go after dogs and humans. And their bite is quite nasty.

2. Beavers

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Beavers may look harmless, but they have huge, razor-sharp teeth that can chomp right through a femoral artery, which is what happened to a fisherman who died from his injuries in Belarus in 2013. They’ve also been known to attack swimmers and go after dogs. So it’s best to avoid these guys.

3. Cows

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Most cows are not violent, but a specific type known as Heck cattle are also called (this isn’t a joke) “Nazi Super Cows.” These cows were bred in Nazi Germany and still roam parts of that country today. A farmer in England bought some of the cows and brought them to the UK, but soon discovered his mistake. He said, “They would try to kill anyone.”

4. Dolphins

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Not Flipper!!! Yes, I’m sorry to report that dolphins are actually pretty deadly, especially to each other. It wasn’t until the 1990s when researchers discovered that male dolphins slaughtered other dolphins, including their own babies.

They’ve also been known to occasionally attack swimmers.

5. Prairie Dogs

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Prairie dogs are plant eaters, but that doesn’t mean they don’t murder other animals. Their main competition for resources on the prairie are squirrels, and they’ve been known to attack and bite them to death, though they don’t eat their bodies.

Prairie dogs that kill have offspring that live longer than non-killers, so scientists are curious whether this phenomenon is occurring in other animals as well.

6. Swans

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Similar to cows, most swans are beautiful, gentle creatures, but there are some that are natural born killers. For example, a swan in Wales named Hannibal killed 15 fellow swans in a particularly vicious manner: Hannibal bit his victims, beat them with his wings, and broke their toes before holding them underwater and drowning them.

So basically, Hannibal is a swan serial killer.

And then there was the swan that was constantly attacking rowers on a river in England, until he and his mate were relocated to avoid further carnage.

Be careful out there! The animals might be taking over!