  Life evolved organisms to adapt dynamically to their environment and
autonomously exhibit behaviours. While complex behaviours in organisms are
typically associated with the capability of neurons to process information, the
unicellular organism Physarum polycephalum disabuses us by solving complex
tasks despite being just a single although gigantic cell shaped into a
mesmerizing tubular network. In Physarum, smart behaviours arise as network
tubes grow or shrink due to the mechanochemical coupling of contractile tubes,
fluid flows and transport across the network. Here, from a physicist's
perspective, we introduce the biology and active chemo-mechanics of this living
matter network. We then review Physarum's global response in migration and
dynamic state to its environment before revisiting its network architecture and
flow and transport patterns. Finally, we summarize recent studies on storing
and processing information to mount well-informed behaviours.
