A jellyfish doesn’t have a brain, but it still knows when to sting you. A sea star can crawl toward food and somehow avoid predators without a single centralized thought. Somewhere in there, something that looks like decision-making is happening, which raises a strange question: can brainless animals actually think?

Scientists say the answer depends on what we mean by “thinking.”

“Brainless does not necessarily mean neuron-less,” Simon Sprecher, a neurobiology professor at the University of Fribourg, told Live Science. With the exception of marine sponges and the blob-like placozoans, nearly all animals have neurons. Creatures like jellyfish, hydras, and sea anemones use what’s called a nerve net. It’s a diffuse web of neurons spread across the body that processes sensory information and

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