Eric Klieg and The Doctor in “The Tomb of the Cybermen”

Doctor, you seem to be very familiar with this place.

Oh no, not really, um, it's all based on symbolic logic, the same as you use in computers. The opening mechanism to this door, an or-gate you call it.

Yes yes, I can see that, but how did you know in the first place?

Oh, I used my own special technique.

Oh really Doctor, and may we know what that is?

Keeping my eyes open and my mouth shut.