Most animals taste something only after it reaches their mouth. An octopus tastes an object the instant its skin touches it, using a sense embedded directly in its arms, long before the information ever has a chance to reach its brain.
Researchers at Harvard discovered the mechanism behind this by studying the two-spot octopus. They identified an entirely new family of sensory cells inside the octopus's suckers, called chemotactile receptors, unlike any known taste or smell receptor found in other animals.
These receptors work differently from human taste buds in a key way. They're built to detect molecules that don't dissolve in water at all, the kind of chemical residue left behind on the surface of prey, letting the octopus tell a live crab from a bare rock without ever taking a bite.
When scientists tested these receptors in a lab, the results were unmistakable. Nothing resembling these receptors exists in human or frog cells whatsoever, meaning this entire sense has no true counterpart anywhere in the human body.
The reason this sense works so fast comes down to where the octopus keeps its brainpower. Roughly two-thirds of an octopus's half-billion neurons are located in its arms, not its central brain. Each arm can process information and react largely on its own.
That independence isn't just theoretical. That independence isn't just theoretical. If one of an octopus's arms is severed, it will still grip almost anything that touches its suckers, a reflex that can persist for hours, with no signal from the rest of the octopus's body required.
Squid, close relatives of octopuses, have a similar sensing system, but with a key difference. Where an octopus feels around to investigate before deciding whether to eat something, a squid grabs first and decides afterward, and researchers say the two animals' differently evolved receptors explain exactly why.
