As humans, we are supposed to have an aversion to slime. It should repel us. Objects and organisms that might be harmful trigger feelings of disgust which keep us away. And, according to the biologist Susanne Wedlich, the common denominator of ‘wide-ranging microbial threats, covering sickness, sex, death and putrefaction’ is their sliminess. It is easy to test this theory. Google ‘slime moulds’ and note your first response. They are gross. But these organisms are worth sticking with. Japanese researchers once conducted an experiment using a slime mould and a map of the country. They put the mould on top of Tokyo and dropped food on to the city’s surrounding towns. A little while later the mould had left a trail that closely replicated the city’s underground system.