The Rebbe -- he of the loudly-shouted opinions -- once insisted up and down it was impossible for humans to have unverbalised thoughts.    From Wordnik.com.  [February 5th, 2005] Reference

“Hum,” I grunted, a considering sound, and read slowly through the German document a third time with his unverbalised but clearly expressed scepticism in mind.    From Wordnik.com.  [O Jerusalem]