Brain

An octopus has roughly 500 million neurons, and more than two-thirds of them are distributed across its eight arms rather than its central brain. The brain issues high-level commands while each arm independently handles the details—a decentralized nervous system.

The brain of a cephalopod is shaped like a donut, with the esophagus running straight through the center. Even in a 300 kg colossal squid, the esophagus is only about 10 mm in diameter—so swallowing too large a piece of food can compress the brain and cause damage.

You can't tickle yourself because your brain predicts outcomes of your own actions and ignores matching sensations. However, schizophrenia patients — whose prediction systems are impaired — can indeed tickle themselves.

The urge to squeeze or bite something extremely cute is a real phenomenon called "Cute Aggression." Yale University research found it's a defense mechanism: the brain generates slight negative emotions to counterbalance overwhelming positive feelings — similar to crying tears of joy.

Purple does not exist in the light spectrum. When red and blue light simultaneously stimulate the eye, the brain creates this color to resolve the contradictory signals.