Underwater breathing aids, such as GILLS, are devices used to allow a person to breathe underwater. GILLS, which are five letters long, are the most common type of underwater breathing aid and are typically found in fish and other aquatic animals. They allow these creatures to extract oxygen from the water and expel carbon dioxide. For humans, GILLS are not a viable option, so other underwater breathing aids have been developed, such as scuba gear and snorkels. These devices allow people to explore the depths of the ocean and experience the beauty of the underwater world.