Here’s a story from bioGraphic about the otter:
Although most European otters (Lutra lutra) tend to prey primarily on fish, some have developed a taste for frogs and toads—a food choice that requires some deft preparation. Because common toads (Bufo bufo) have toxins in both their skin and the glands on either side near the front of their bodies, these resourceful otters use their sharp teeth to remove the skin from the back half of the toads and then eat just the hind legs. While common frogs (Rana rana) don’t have toxic skin or glands, most otters appear to not know the difference, and generally play it safe by following the same food-prep routine they use on toads. In river systems where the otter’s traditional foods—including salmon, butterfish, and eels—are in decline, amphibians have become an increasingly important part of their diet. At the same time, the otters have become increasingly resourceful. In recent years, a number of individuals have been observed completely removing the skin from frogs and toads, an extra step that allows them to eat both the front and hind legs of their amphibian prey. Photographer Sven Zacek spent 10 days watching this female otter hunt along a river in southern Estonia. Zacek recounts that this proficient hunter brought up a meal after every dive—and on almost every occasion, that meal was a frog.