Then they said to the ear: 'Do thou sing out for us.' 'Yes,' said the ear, and sang. Whatever delight there is in the ear, that he obtained for the Devas by singing; but that he heard well, that was for himself. The Asuras knew: 'Verily, through this singer they will overcome us.' They therefore rushed at the singer, and pierced him with evil. That evil which consists in hearing what is bad, that is that evil.

In plain words: Then the gods asked the ear to sing. The ear kept some of the pleasure of hearing for itself. So the demons struck it with evil, and that is why we can hear bad things.