Why does a girl seem interested but do things that imply otherwise?

It has happened to several people, both men and women.

1-This girl does things like telling me not to touch her and she walks away from me or removing my hand from her shoulder and then things like one time we were sitting across from each other and she leans forward until she is on top of my legs while looking at me and talking to me.
2-A girl started touching me in class, calling me baby and heart when I wrote to her on WhatsApp, once she came to the classroom and looked at me smiling for several seconds, noticing things I did for no reason, but the girl never writes to me, she doesn't join me in her social group and she lied about not having Instagram when I asked her

Why does a girl seem interested but do things that imply otherwise?
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