Gills are special organs found in many aquatic animals, like fish and amphibians, that allow them to breathe underwater. They work by extracting oxygen from the water as it flows over them. This process is essential for these creatures to survive, as they need oxygen just like we do. In addition to fish, some invertebrates like crabs and octopuses also have gills. These organs come in different shapes and sizes, depending on the animal. Gills are usually located on the sides of the head or under the body, making them well-suited for life in water.