A question that has exercised literary pedants down the years is why Robinson Crusoe found only a single footprint on his desert island. A shipwrecked sailor whose other leg had been taken by a shark? A stray member of some strange tribe of hopping cannibals?

A persuasive solution is offered by Professor John Sutherland in his second volume of literary puzzles, Can Jane Eyre Be Happy? (Oxford University Press £4.99). A lone savage has rowed up to the steeply inclined beach to investigate Crusoe’s canoe. Finding no one to eat and nothing to pillage, he pushes off again. The tide subsequently washes away all traces of his visit save for one footprint, where he stepped momentarily above the high-tide mark.

I prefer the less ingenious but more thrilling explanation that Daniel Defoe, instinctively or not, chose ‘a single print of a foot’ rather than a trail of footmarks or (he keeps this for later) the remains of a cannibal feast because, like a matchstick on the moon, it is more spine-tinglingly effective than detailed evidence of human presence could ever be.

That solitary footstep was a giant leap for Defoe, transforming him, in one bound, from pamphleteer and scribbler into one of the