Yikes. After chancing across a photo post on Facebook of a see-through glass eel, I just had to find out more about these utterly transparent creatures. According to an ex-curator of Yale Peabody Museum of Natural History, this glassiness happens in the first two stages in the life cycle of your American Eel-next-door. In their second stage, they gain their adult shape and migrate to estuaries on the Atlantic coast. Only in the third stage do they gain both colour and size. National Geographic agrees.