Girl's Behavior

Why was a girl staring at me while talking to her friend, looking at me then quickly turning away? What was she trying to do?

I ran some errands with my roommate and noticed someone staring at me. When I turned around, a girl’s eyes widened, and she smiled before quickly turning back to talk to her friend. She seemed torn between focusing on her conversation and sneaking glances at me. I just looked at her, wondering, What do you want? Why are you staring at me?
Why was a girl staring at me while talking to her friend, looking at me then quickly turning away? What was she trying to do?
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