Nerida had always lived in the giant treehouse that her grandfather had built in the heart of the kelp forest. The treehouse was not made of wood, but of woven sea grass and polished shells that glowed softly in the dim ocean light. However, Nerida rarely left its safe branches, because she was afraid of the open water beyond. Her only companion was a small, wise octopus named Cephalos, who often watched her play chess on a barnacle-covered board.
One evening, as Nerida moved her knight, Cephalos said, "Your brain is the control center of your body, just like the queen controls the chessboard." Nerida paused, her fingers hovering over a pawn. "Every time you plan a move, millions of neurons send signals through your nerves," Cephalos continued. "These signals travel from your brain to your hand, and back again, helping you coordinate your thoughts and actions." Nerida had never thought about her own brain before, but now she imagined tiny messengers racing inside her.