Why does she lean against me while laughing?

I'm a guy, my close girl friend does this thing where if she's laughing she will sometimes lean on me with both hands and bury her face against my arm like she trying to hide her face. I have no issue with it, it actually makes me laugh when she does it. I'm just wondering have you ever done this or know someone who does this and why?
Why does she lean against me while laughing?
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