An unexpected note of poignancy greets visitors to the museum of the world's largest car company. In the cavernous lobby, a lone trumpet plays the mournful opening bars to Over the Rainbow, a plea for escape from the dreary, difficult realities of the present. The song is performed by Partner Robot, Toyota's showcase humanoid robot, on a giant screen that hangs over a showroom full of the company's world-beating products, cars that have become household names: Prius, Lexus, Corolla.