What are signs a shy girl in class likes you?

their is this girl that always sits behind me, when I first look at her she would always look down. so I thought she was not interested until I caught her looking at me then looked down when I notice. she is dead quiet and I can hear her fidgeting with her keys. until recently when the sign in role sheet was passed, she tapped me rapidly with the paper so I looked back and notice she was looking down so I smiled. she then starting laughing and became apologetic then I grab the paper and said thanks. from then on I can actually hear her voice as she silently and verbally answers the questions written on the board.
What are signs a shy girl in class likes you?
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