The Galapagos Islands are home to incredible animals and diverse life, both above and below the surface of the ocean. Scuba divers come from all over the world to explore the depths and observe animals like whale sharks and other shark species up close. These divers have entered a cave that is 20m (60 feet) below the surface. They turn on their lights and enter, unsure of what to expect. The scuba diver discovers sleeping white tipped reef sharks, a gigantic moray eel, and a large Pacific green turtle, also taking a nap. This seems unusual for sharks to gather and sleep because we were once under the mistaken impression that sharks would not be able to breath unless they are in constant motion to keep water moving over their gills. Most fish possess the ability to pump water through their gills but many sharks are unable to do this. Hammerheads are a good example and it was once believed that they did not sleep since they swam constantly. Sharks that constantly move are able to rest half of their brain at a time, entering a state of reduced consciousness. They are still able to avoid predators or objects as they swim, because half of their brain is awake. These white tipped reef sharks do not need to keep moving and they are able to sleep fully while sheltering on the sandy bottom of caves like this one. The turtle will also sleep for a brief period but it will need to go to the surface for a few breaths of air. As we discover more about this exciting and mysterious realm, we also learn that there is much more that we do not understand. New species and new behaviours are being discovered constantly. As demonstrated by these sharks in this cave, most of the animals in the underwater world will do us no harm if we maintain the appropriate level of caution and respect. It is wise to remember that we are the guests in this beautiful domain.