Slime mold is weird stuff: despite having no brain or nervous system it's ruthlessly efficient at hunting down food. So efficient that if you lay out food for it in the pattern of major cities across the US, it grows in the exact same paths as the highways we've already built.
Andrew Adamatzky, a researcher at the University of the West of England, UK, takes a petri dish of agar and holds it over a map. Then, he places oats where each of the major cities is, and dollops a lump of slime mold at the nation's capital. The networks that the slime forms pretty much tally exactly with the roads humans have built between the real cities.
If you don't quite believe that, I don't really blame you. But he's done the same experiment using maps of Canada, China, Australia, the UK, France, and a bunch more—12 in total—and the same thing happens each time. He speculates that it's because roads are actually based on unplanned paths that were also originally chosen by living creatures—whether humans or roaming cattle. Whatever; I just think it's amazing. [arXiv via New Scientist; Image: Andrew Adamatzky, University of the West of England]