"Mauna means “silence.” Unless one becomes silent, he cannot think completely about the pastimes and activities of the Lord. It is not that because one is a fool and cannot speak nicely he therefore takes the vow of mauna. Rather, one becomes silent so that people will not disturb him. It is said by Cāṇakya Paṇḍita that a rascal appears very intelligent as long as he does not speak.
But speaking is the test. The so-called silence of a silent impersonalist svāmī indicates that he has nothing to say; he simply wants to beg. But the silence adopted by Kardama Muni was not like that. He became silent for relief from nonsensical talk. One is called a muni when he remains grave and does not talk nonsense."
(Srimad-Bhagavatam 3.24.42)