I never knew this until I accidentally discovered it, but you can lock unlocked doors with any key. Presumably this means it'll only be openable with that key, which oughta be handy when escaping. Was this common knowledge that slipped by me or is it just one of those cool little extra?

EDIT: I can't get it to work now. It might only work on doors you lockpick?

I can't experiment with it now, but IIRC you can re-lock doors with the key you opened them with (or with the key that belongs to them, if unlocked it with lockpick). Guards can open re-locked doors if they have the key for it - though I recall stealing a guard's key and him still being able to open locked doors, so it might only work against guards who don't have the key at all.

Those angel children totally creeped me out. So that's what they do? I had already taken out most of the guards on that floor when they showed up. Man.. that was an awesome mission.