The animal that can sleep for up to three years is the land snail. During periods of unfavorable environmental conditions, such as drought, some species of land snails enter a state of dormancy called estivation. During this time, they can seal their shells with a layer of mucus to retain moisture. This process allows them to survive for extended periods without food or water. While in this dormant state, their metabolic activity significantly slows down, enabling them to endure long periods of extreme conditions and emerge once the environment becomes suitable again.