Basically obvious signs of attraction from girls.
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When she's around you, she will seem to stand taller, pull her shoulders back, and pull her stomach in. You can even try to be slick and check out her posture when she walks away from you, or when she doesn't know you're around.
You'll see her licking her lips, touching her neck or lifting her head so that more of her neck is exposed. She may lean toward you more, or move closer to you. She might lean in to whisper as an excuse to get closer.
Flared nostrils can be a sign of interest, although this might be hard to detect without looking a little too interested in her nose. She might start playing with her hair and wiping imaginary dust off your clothes.