This is a myth.

How true is it, on one knows.

Statues absorbed light from the moon and sun everyday and it gains energy slowly day by day.

Inside the statue is a demon, i dun noe y it cannot be a good guy and must always be a demon.

And when this demon has gained enough energy, it will break free.

So when this is about to happen, the god/heavens would of course know about it, and therefore would struck a bolt of lighting to the statue killing the demon inside it.

My dad said that last time at chinatown, got the Hindu temple.( A very famous temple which is still there today )

Got alot of cows' statues on it. 

Rumours has it that at night, one of the cow statue head would turn.

Soon after this, lighting struck the temple and that particular cow's statue de head was struck off.

Could the merlion insident recently been related to this myth?

My dad was telling me all these stories while we were having dinner.

He said if you watch xi you ji ( journey to the west? ) you should know.

HAHA..