Talking is the business of tongue, and tasting is the business of tongue. So you engage the tongue in the service of the Lord by glorifying. Whenever… You take a vow that "Whenever I shall speak, I shall simply speak, glorifying Krsna, nothing more." That is tongue control. If you don't allow your tongue to speak anything nonsense, gramya-katha… We sometimes sit together. We talk so many nonsense. That should be controlled. "Now I have engaged my tongue for the service of the Lord, so we shall not talk anything of sense gratification." This is controlling the tongue. "I cannot eat anything which is not offered to Krsna." This is controlling the tongue. So these are small techniques, but it has got great, great value so that Krsna will be pleased, the austerity, and He will reveal.

(Srila Prabhupada — London, August 4, 1973)