kael pretty much nailed it. So much of the game is body language but especially eye contact. The more you are out in field the better instictivly you will be at knowing instantly if a women is interested in you & how to instantly convey interest without saying a word.
I thought I had a good grasp on this 6 months ago, but the thing that has recently taken my game to another level is basically the squinting an leaning your head back to look down at them a little. I'll add many chicks will squint back at you if they are into you if they are confident or comfortable with you. Others will look down submissivly and then quickly look back up (especially when 1st seeing you if you are projecting confidence), make sure you are still looking at them I have found when they look back up , blows them away. If they have no interest they basically just turn their head. If you carry yourself right though it's hard not to get some response.
Here are 2 video's as good as I know to describe it.
Squinting. Lots of it by Leto, some even over the top exagerations of. Check out the squinting at :46 and the tone tilt to the side especially. Watch his eyes.
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http://www.youtube.com/watch?v=2KO2xxpr118[/youtube]
Now the head tilt back. Cajun from Keys to the VIP nails it. 2:20 on
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http://www.youtube.com/watch?v=ivnXzgFIEvM[/youtube]
Ill add if you If you carry yourself a certain way or sit a certain way, YOU will get looks from women. I can tell almost instantly now if I see a women is into me. looking at me out the corner of her eye body turned a little, especally and especially if they let themselves be caught doing it. I've learned to sit now where I look so comfortable I have had girls open me with " you look comfortable". That told me I was doing something right. Walking is where I get the most attention though, thats when you can really make eye contact.
The squinting is where it's at guys. I've even had a couple girls that were VERY attracted to me like squint and snarl at me or look like they wanted to bite me. Very animalistic