CAN HEAR A FAINT METRONOMIC TICKING, coming in pulses, like a clock on its last wind. Here, in the swampy rainforest of South America, this curious sound doesn’t make sense. Maybe it is an insect – a cricket or cicada – but it seems to be coming from underwater. Standing at the edge of a clear forest pool, I kick some leaves around with the toe of my boot and detect movement. Is it a