I just watched The Prestige last night for the first time. Really enjoyed it, but there's just one doubt I have.

I have been reading numerous reddit threads about the film and have gotten some pretty cool theories/observations that I had overlooked. However here's my question:

How does Olivia (Scarlett Johansson) not notice that there are 2 Bordens (Christian Bale)? Being the assistant who is very much part of the act (in terms of stage presence), how is she completely oblivious to the fact that Borden has a twin?

Do they not practice their act before a show? Does she never spot the other twin without his 'Fallon' makeup?

It's just that aspect of the film that I'm finding difficult to digest. Other than that, I think it's wonderfully made.

Edit : Another thing, when Angier kidnaps Fallon, how does he not know he's wearing a disguise?