This may seem hard to believe, but the adorable dolphins you swim with at Sea World may not be as innocent as you think. According to marine experts, the bottlenose dolphin might actually be the only animal on earth that murders fellow underwater inhabitants for the sheer fun of the kill.

The first clues arrived in 1997, when a succession of dead porpoises were washed up in the waters of Scotland's east coast and the shores of Virginia. Biologists found that the porpoises had died of broken ribs, damaged livers, and imploded lungs, which served as tell-tale signs of prolonged, focused attacks. Although the motives were unclear, the teeth marks discovered on the bodies were a sure-fire sign: the prime suspects of these murders were bottlenose dolphins.