Over a beer Jim celebrates his first draw against an international chess master, the rank just below the coveted title of grandmaster (GM). I joke that GMs are next on the menu. “No,” he says, “these guys see things on the board which us mortals can’t see.”

A magician asks a spectator to name any playing card. The five of hearts. The magician opens his wallet, then the zipped compartment within, and pulls out the chosen card. After the show three magicians search in vain for a solution. An experienced magician joins the group and immediately suggests an ingenious and plausible method.

Harvey Cushing, in one of his essays, wrote of a patient who was admitted to hospital with an unexplained fever.1 Various tests were done: blood, urine, sputum, stool, cerebrospinal fluid. Specialists were called in. Meanwhile the fever continued. A country doctor who was visiting the hospital walked past the patient’s bed and said, “I am surprised to see that you still have an occasional case of typhoid fever in your …