Some artefacts are like old friends. Even after long absence one takes up where one has left off and departs feeling refreshed and enriched. I am unable to enter the Ashmolean museum in Oxford without revisiting a pre-dynastic Egyptian hippopotamus I first met over 50 years ago. Its wrinkled head is raised in confrontation, its gaping jaw functions as a spout full of animal aggression. The round, swelling body taut with energy, full of power. It is made with coarse tan clay containing vegetable matter that has burnt away, leaving patches of carbon grey pitting the surface, reinforcing its visceral appeal.