The Doctor grinned even wider, and noticed that the rubber lips around the robot's speech loudspeaker were doing the same. 'Fascinating. I suppose that's to reduce the common fear that people have of robots, the lack of empathy and expression. You're able to imitate people!'

The robot stood facing him, arms akimbo, its face a picture of mechanical amazement. 'Am I?' it said with a wide-eyed grin. It slapped its forehead again with a tinny clank.

'Yes,' said the Doctor. 'But don't overdo it.'