From the octopus that stole fish from a tank to the monkeys that blackmail tourists for treats: How scientists have discovered the astonishing masterminds of the animal kingdom

Clever Hans, a performing horse, drew amazed crowds wherever he went. With his owner Wilhelm, a maths teacher, he put on incredible displays of arithmetic, beating out the answer to sums with his hooves. Hans even appeared to be able to read, though sceptics insisted the horse was merely responding to signals given by Wilhelm, touring Germany before the First World War. However the trick was done, neither the animal nor the teacher would have been surprised by news this month that horses are more intelligent than previously guessed. Researchers at Nottingham Trent University taught 20 horses to touch cards with their noses in return for treats.