The internet loves animals, anything from dolphins and sloths, and it really loves cats. But just in general, we have a strong affection for just about anything cute and fuzzy. This fondness can lead us to ignore the strong evidence that many of these cute furballs are just monsters. Yet, even now, monsters deserve protection, and efforts to save these creatures from extinction are worth supporting. But we can still be aware of the evils our furry buddies are capable of. Here are seven of the more disturbing adorable species:

Every other terrible thing you can imagine a dolphin doing, they’ve done.  Dolphins are also known to pummel baby porpoises, which is strange. They don’t even eat the porpoises, the porpoises aren’t rivals for resources, and the porpoises don’t offend them at all. Dolphins are just plain ol’ mean.

The terrifying part is that dolphins are very, very clever. That only makes them more efficient recreational killers.

Hippopotamuses are tough to study in the wild because they attack humans who get too close and because so much of their lives take place in the water. Hippos are vicious and like to maul people, sometimes without any provocation. They’re also herbivores. They don’t eat the people. They’re just aggressive jerks.

A paper by the Journal of Human Evolution examined wildlife attacks in Uganda from 1923 to 1994. They mostly centered on large carnivores like lions and leopards but inserted some data on hippos too. They discovered that hippo attacks had the highest mortality rate of any animal! 86.7 percent of the 30 hippo attacks examined were deadly, compared to 75 percent of the lion attacks and only 32.5 percent of leopard attacks.

Polar bear violence is pretty standard, as these things go. They attack and eat seals. Males compete viciously over female partners. Standard stuff, all around. But polar bears also incline towards cannibalism. A 1985 paper by Mitchell Taylor, Thor Larsen, and R.E. Schweinsburg reported dozens of polar bears eating each other.

More recent research continues to find polar bears devouring each other, with some researchers arguing that the practice is rising due to global warming. “As the climate continues to melt the ice, thus meaning seals are less available earlier in the summer, meaning the frequency of intraspecific predation and cannibalism may increase.”

When it comes to mass destruction, no species come close to humans. Humans might be becoming less cruel toward each other; both individual and state-level violence is on the decline. But humans are pretty expert when it comes to killing other animals.

A World Wildlife Fund study recently found that all mammals, birds, reptiles, amphibians, and fish in the world fell because of human exploitation. In other words, humans are the driving factor behind the sharp drop in all populations. In fact, humans may be causing the sixth mass extinction event of the past half billion years.