"Stage directions can also unintentionally indicate dishonesty. If you mention an incidental action at the wrong moment, it can be taken as a significant comment on the dialogue. Those which show that a character is nervous, or which seem to conflict with the emotion that the dialogue is meant to express, are read as signposts of dishonesty. 'Of course I'd tell you if something had happened to Fluffy,' he said, fidgeting with the napkin tells the reader that Fluffy is no more."
Liv: You're very bad at lying to your friends. You've got a tell.
The Doctor: A what?
Liv: Like in card game. A change in your behavior that gives you away.
The Doctor: Really? That's wonderful! What is it? No, no! Don't tell me. Do I... rub my nose? ...Ruffle my hair? Ah! I hope I get a twitch!
Liv: Uh, no. You just look terrified... and guilty.
The Doctor: Oh... That's disappointing.
The Doctor: A what?
Liv: Like in card game. A change in your behavior that gives you away.
The Doctor: Really? That's wonderful! What is it? No, no! Don't tell me. Do I... rub my nose? ...Ruffle my hair? Ah! I hope I get a twitch!
Liv: Uh, no. You just look terrified... and guilty.
The Doctor: Oh... That's disappointing.
