Why does he blush and smile when I laugh?

There's this guy who I'm aquantices with at work and sometimes. I've noticed that recently when I start flirting with him and get the giggles or laugh, he laughs with me or smiles. Sometimes he blushes when he laughs with me and goes 'what's so funny?' in a playful way. I have noticed that when he stares at me sometimes he will start blushing after a while. I don't usually say or do anything to make this happen. Also, sometimes mid way through conversation he will start blushing.

I haven't noticed him blushing around anyone else, and he seems really confident in the presence of other people

Why does he blush whenever I laugh?
Why does he blush and smile when I laugh?
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