Science is always telling stories. Whether in the creation myths of evolution or the Big Bang, or in the eureka moments of science history, narrative – just as much as metaphor – is a key tool in the scientist’s surprisingly literary toolkit. Perhaps the most interesting use of story is the thought experiment, the intuition pump, that draws on the most instinctive parts of the imagination to crack otherwise perplexing problems. From Newton's Bucket, to Maxwell’s Demon, from Einstein's Lift to Schrödinger’s Cat – all are examples of 'fiction' being used at the highest level, not just to explain, but to deduce, to prove. This story is taken from a unique anthology, Thought X, in which authors have collaborated with leading scientists, to bounce literary, human narratives against purely theoretical ones, alloying together real stories with abstract ones, to produce truly extraordinary results. This story by Robin Ince is inspired by 'The Spider in the Urinal' thought experiment, and is accompanied by an afterword written by professor Glen Newey.