Daisy's gift / Claire Guest.

A dog's sense of smell has long been harnessed to help humans by sniffing out drugs or explosives, guiding the blind along a busy pavement, or by alerting the deaf to doorbells and telephones. But Claire Guest, Chief Executive of the charity Medical Detection Dogs, has proven that in controlled scientific conditions, dogs can detect cancer cells where technology fails. Even better, their methods are non-invasive. But it's not been an easy discovery. As well as depression, marital break-up and breast cancer, Claire has had to deal with sceptics who believed her research was too 'bonkers' to be used in practise. But the evidence is overwhelmingly promising: one dog has developed a 93% accuracy at detecting bladder, prostrate and kidney cancer, when other non-invasive tests only have 25% accuracy.