Sea squirt
The sea squirt search for a rock to call home, and when they find it they don't need their "brain" anymore and so they eat it. The brain has toxins in it that are very deadly to any predator but the taste is said to be magnificent and so some people attempt to follow seasquirts until they start to eat their brain as they notrlize the toxin as they eat the brain and if caught before they digest the brain the brain can be extracted and eaten even without cooking. The sea squirt will soon die afterwards as the nutrients from the brain are critical to it's lifecycle.