You're not supposed to know.
They're exerting power - sex power - over you.
Learn to ignore it, and you will become more powerful than you can possibly imagine.
Having your wife there makes these girls easier to ignore.Also makes the back of your head ache if you don't.
Fundamental Leykis 101. If you can ignore a good looking female, you already have one leg up (pun intended) so to speak. When I was younger and still in play, we had two favorite techniques:
One was to whistle/hoot not at the girl in question, but something other like a friend, car, etc. Once they got over the intial deflation that they weren't the object of desire, then you could move in after they had been softned up a little bit.
Two is more traditional - pay attention to the tag-alone uglier friend. Those who undestood the inside game actually appreciated this techniques, as the less-attractive one got some needed face time that they normally wouldn't get, and the prettier one got to sit in on the 'interview' to see if the suitor was suitable.
Anyway, for all the youngsters out there, I'm sure these techniques are still in play.