This screensaver shows you off the images of dreadful sharks that are so big and aggressive to pesent the threat to the humans. Dreadful sharks were known to mariners as "sea dogs" since the past due to their mighty jaws and terrible teeth. You will see the blue shark, great white shark, mako shark, silky shark, reef shark and hummerhead shark. Some of them can attack on humans unprovokedly, some can attack by mistake. Beware of sharks when you are swimming in dangerous waters!