Jimi:This input comes with the disclaimer that not all chicks are the same, so it could be totally wrong.
I don't stick my hands in a guy's pockets, feel around, check out the goods, and in general play with any part of his body unless I'm interested in something. Like, oh, screwing his brains out until he's ready to die from exhaustion.
You should put the feelers out. Watch TV with her and sit close. Stand behind her and put your hands on her shoulders. If she's ok with that, rub them. It'll progress naturally.
Backrubs are notorious for going from 'just a friendly shoulder massage' to 'tonsil hockey world championships' if there's any spark of mutual interest at all. Also, if done to a friend, it's not usually a 'suspect action'. I doubt it'll freak her out too much.
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kuru
'dancing is the vertical expression of horizontal desire.'
-robert frost