Guy's Behavior

When a girl is nervous around a guy, does it mean she won't smile around the guy? (please read details)

there is a girl who is not the loud type nor is she the type to do the unexpected. This girl also smiles when she talks to anybody EXCEPT me. I don't think she hates me because she says "hi" to me every so often (this, I believe, is a good sign because I only know 2 other guys other than me that she says hi to and another thing is that I'm not one of her friends thus making her "hi"s a better sign. she hardly ever talks to other guys but she won't hesitate to ask a guy a question like homework help questions). today I talked to her but she wasn't smiling at all when she talked to me and her voice was a lot more quiet than usual (I've heard her talk to other girls and guys and she was definetely a lot more quiet when she was talking with me). She also only gave short responces to my questions during our talk. Do you think that there is something about me making her uncomfortable? is she nervous around me? another thing that happened today was that I had to sit in an empty desk next to her today in one of our classes and she was fidgeting with her glasses case a lot (she kept prying it open and closing it). in the other two classes that I had with her afterwards, I looked at her from my seat and she wasn't fidgeting with her glasses cases at all in these 2 classes.
When a girl is nervous around a guy, does it mean she won't smile around the guy? (please read details)
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