In the quiet sprawl of forest floors, a brainless, single-celled organism has been solving mazes — and in doing so, has unsettled one of science's most foundational assumptions. Researchers studying slime moulds are now confronting a question that reaches far beyond biology: whether intelligence is a property of neural architecture, or something that can quietly emerge from any sufficiently adaptive system. The debate is not merely semantic; it asks us to reconsider what it means to think, and which beings and machines we might one day recognize as doing so.