Why does she giggle whenever we talk?

Hi, people. I need some help to understand feminine behaviour.

Some background first. Half a year ago I (33 m) met a girl (23 f) at an extension class. We bonded over our similar academic interests and international experience. I asked her out, but things didn't work out after the second date. She didn't want anything serious and I have the impression that she got a little bit intimidated by me having more experience in life and professionally (we are both college educated, but she was finishing her first master and I am doing my PhD). We were in amicable terms, but she ghosted me shortly afterwards and I hadn't seen her until today, in the street.

Well, I digress. When we first met I remember how she giggled a lot, and not only when I said "funny things". When I told her about my plans for life (which are very ambitious) she giggled and when I complimented her (which, naturally, she liked), she giggled.

Today we saw each other in the street and she came to greet me. We talked a little bit, and when I asked about her job (she is looking for one now) she gave me her traditional giggling. So, ladies, I want to know what shall I make of her cute nervous laughing. Why do women in their early twenties giggle when they do it? Why does she do it whenever we talk. To be fair, I don't have many places to make a comparison because none of my female friends are the giggling kind.

PS: I know there is no prospect of a relationship here. She is one of the best persons I've met, but some things are just not meant to be and I am well aware of the obvious maturity issues here.

Why does she giggle whenever we talk?
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