Why the girl who rejected me sometimes looks at me and other times avoids eye contact?

She rejected me but we still are friends, sometimes she stare at me and talk me without problems but other times she avoids look at me or make eye contact even though we are talking close each other, or when someone say a joke about me, she avoids looking at me too even she is laughing. I don't flirt her, I treat her like a friend
Why the girl who rejected me sometimes looks at me and other times avoids eye contact?
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