When Macbeth was told he had nothing to fear until the local woods started ambling up to his castle, the tyrant sighed with relief, for "who can impress the forest, bid the tree unfix his earth-bound root?"
Macbeth obviously had never been to Barro Colorado Island in Panama.
It is 9 p.m. and as dark as a witch's mummy, but in the cone of light cast by my headlamp, parts of trees seem to be unfixing themselves and wandering at will. A four-inch twig buzzes overhead and thuds onto a nearby branch. A lime green leaf scratches through a pile of brown leaves, finds nothing of interest, and crawls toward another pile.