Ina (The Polynesian goddess of light) and the Shark

A long time ago there was a beautiful maiden called Ina,
who rode upon a great shark to seek her boyfriend lover,
the god of the Ocean, on another island.
During the journey she was hungry and decided to open a coconut she had brought along. But she didn't have anything to open it with. Then she suddenly got an idea.
She cracked it open on the sharks head.
The shark then shook her off his back and ate her.
That's how sharks got a dent in their heads.