Is it just my imagination...
I was watching this recently and paused the TV for some reason. When I came back to it I realised I'd paused it on the moment Evey takes Valerie's note from that hole in her cell. You only see a small part of her face but I could have sworn it was actually Hugo Weaving's face, not Natalie Portman's.
I know some directors do this, a very subtle hint of the truth or something will happen or will be revealed later: Christopher Nolan in Memento, Bryan Singer in The Usual Suspects.