Well, she might have known that Boomer did not have a twin. Also, it's possible that the uniform they wear (or some insignia or element of it) is specific to Galactica.

eta: Plus she no doubt had Cylon duplicates on the brain, as she (I think) saw another Six on Galactica.

Actually, I really quite liked Starbucks instantaneous running through a sort of:

Another Boomer? Boomer's a Cylon? Boomer's a Cylon, kill her!

thought process.

There's also the "everyone on this planet is an enemy" thought process.

Hmmm... I bet that would process quicker....

There's also the "Another hot chick! No! I must be the only one!" thought process.

OK, maybe not.

The problem with the "kill everyone!" thought process is that she didn't seem to consider Helo an enemy at any point.

We're also talking about a damn good fighter pilot, so I can buy that she'd get from A to C faster than most of us.

Maybe Starbuck just has good instincts? I think she, at least, is used to going on her instinct which is possibly why she was able to realize that 2nd Boomer means Boomer is a cylon very quickly.

(Also, weren't there "Boomer is a cylon" rumors earlier in the season? I mean, aboard Galactica.)

so I can buy that she'd get from A to C faster than most of us.

This. She was in full-on adrenaline battle mode, so I bought her thinking really fast.

(Also, weren't there "Boomer is a cylon" rumors earlier in the season? I mean, aboard Galactica.)

Someone made that joke during 33, because she never seemed to get tired. But I think it was just a joke.

just watched BSG. kept waiting for the unexpected and I was not disapointed. Boomer's turn was unexpected, but no tunexpected. the timeing was lovely.

I thought Lee's behavior was very much in character - he is a rules player and doesn't like when things are unfair.

I really liked the idea that I really could pick sides beween the pres and adamas