Glass eels are well named, every detail of their bodies can be seen through their skin - even blood flowing through the filigree of capillaries in their fins. Glass eels wait for darkness to hide above them from gulls and other fishing birds before they continue upstream on their migration. Birds may be asleep, but estuary perch hunt around the clock. After travelling in freshwater for two weeks, the young eel changes again - she loses her see-through look and becomes a brown-skinned elver. She feeds voraciously, any worms encountered en route are quickly snaffled up. But her food doesn’t have to wiggle and squirm, she’s a skillful scavenger as well. There’s food at a riverside barbecue, but how can she get it? A scent trail leads her to the gristle from the hamburger thrown into the river.