The Doctor picked up a strange object, studied it carefully, and stuck out his tongue, but before he could try an experimental lick…
“Oi, Spaceman, why d’you go around licking everything?” Donna asked, wrinkling her nose in distaste.
“Tongues are very sensitive organs I’ll have you know, especially Time Lord tongues. I can tell a lot about things with a quick lick, analyse them right down to the molecular level, tell what they are and what they’re made from in an instant.
So saying, he gave the thing a good lick.
“So what is it?”
He pulled a face. “Sour!”