Girl's Behavior

Girls, Why do her eyes sparkle or seem to shine when she looks at me?

There is this girl who I'm almost positive likes me as she has shown a lot of signs. I think she also knows at least part of my schedule because she has walked past 2 of my classes now and looked at me. The second time which was yesteday i was rather close to the door and when she looked at me I could see her eyes sparkle. What does this mean?
Girls, Why do her eyes sparkle or seem to shine when she looks at me?
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