Want to study sperm whales up close? You need to learn to free dive because they are afraid of the bubbles produced by scuba gear!

I'm amazed they'll let you free dive near them. They're friendlier then I thought. 

If it's not obvious from the description... free-diving is crazy dangerous! The female world champion of all time just disappeared on an "easy" dive not long ago...

So sperm whales will let you near them if you demonstrate that you're willing to do something dangerous. Perhaps they, too, love danger.