Myth are clues to the spiritual potentialities of human life.
Nandi is the sacred bull of the hindu god Shiva.

Bull is symbolised here to your own spirit,your own bliss.just like a bull is free from the bondage of society or rules.your spirit is free from the bondage of instinct, which you need to survive.

Shiva is associated with the spiritual realm.

Follow your bliss ,you will get there.

there is a proverb in india.
If you say something you wish in the ear of Nandi(sacred bull).Shiva will fulfill it.
So,it is true in the metaphorical way.
if you are going to say something to Nandi ,it will never be fulfilled.

Spirit symbolizes in other religions like neutral angles,