His frown might make it obvious he's not sure that what he's saying is true, but how would he know. He can't read, so maybe you don't have to see it to know what he's saying. Or trying to say while he's reading it.

"You can read bumps like letter?" He is just learning more and more every day.

"I guess? He's Mexican." He shrugs. "Vasquez is from Mexico, and he's always saying things to me in Mexican and I want to know what he's saying."