Bartholomew's language (The Slitheen Excursion)

During her first encounter with the Tenth Doctor, June witnessed him speaking to an alien by the name of Bartholomew in an alien language. To her, the language consisted of "clicks and whistles". When the Doctor realised that she was listened, he was able to speak English during the conversation, so that June could help. (PROSE: The Slitheen Excursion)