Gnaw chunks out of the piano

Hi,

This is an expression, which is being used when trying to explain how mad a man gets by a superstitious action of his wife.

"...and anyway, it didn't do any harm. And Michael would nod, walk quietly out of the room and go gnaw the chunks out of the piano."

I thought that it just refers to his anger. Because he finds it really irritating but I wonder if there were any clearer explanation to this.

Thanks in advance,

Dilan.