When frogs eat a meal that tastes bad or is poisonous they can vomit it up. Some frogs can even vomit up their whole stomach, use their front right leg to wipe their stomach clean and swallow their stomach back in place. They use their front right leg because their stomach is on the left side of their body. When the stomach is hanging out of their mouth, it pulls to the right (since the membranes holding the stomach in place are shorter on that side). The front right leg can reach the stomach and clean out whatever nasty meal was inside.