Why do octopuses have eight arms? The better to punch fish with, new research reveals.

These brainy cephalopods sometimes team up with fish to find food; hunting collaboratively like this allows them to cover more area, and it increases their chances of catching prey. However, when big blue octopuses (Octopus cyanea), also known as day octopuses, are displeased with their fish partners, they demonstrate their ire by suddenly punching the fish in the head.

The octopus lashes out using “a swift, explosive motion with one arm,” in an attack “which we refer to as punching,” scientists wrote in a new study.

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