What does it mean if a girl smiles and bites her lower lip?

So I have a female friend that looks at me and smiles while biting her lower lip.

She mostly does this is a response after I joke around with her or tease her about something.

I also notice she does this when she's thinking/studying too (she doesn't smile while doing this just bites lip)
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+1 y
I feel like some people are misinterpreting it. When I say bite lip I don't mean biting it like biting the skin off. I mean like the classic lip bite you would see in movies and stuff
What does it mean if a girl smiles and bites her lower lip?
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