Ellen Ruppel Shell's Slippery Beast is a fascinating account of a deeply mysterious creature--the eel--a thrilling saga of true crime, natural history, travel, and big business. What is it about eels? Depending on who you ask, they are a pest, a fascination, a threat, a pot of gold. What they are not is predictable. Eels emerged some 200 million years ago, weathered mass extinctions and continental shifts, and were once among...