Girls, Why she smile nervously when she passed me?

There’s a girl that seems really shy at the gym. I think she kinda cute so sometimes I would check her out. Anyway she kinda noticed me checking her out when she sees me. And she would look at me a few times but she seems too shy to make eye contact.

when I was driving in to the car park. She was looking to cross the road so I stopped to let her pass but she didn’t expect me to wait for her and then when I waved her to cross she kept smiling nervously to herself.

Girls, Why she smile nervously when she passed me?
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