Last week we discovered beluga whales say hello by waving and blowing bubbles. Now it's the turn of sea turtles to show us their underwater greeting. And if this YouTube video is anything to go by, the shelled ones apparently do it with a 'high five' style flipper slap. In the 35 second clip, which is sure to go viral, two turtles can be seen gracefully swimming towards each before both extending a flipper. The pair then give a perfectly timed high five before spinning around and continuing to swim together.