Why does it mean when a girl whisper something to her female friend right in front of me?

I have seen girls do this a few times. What makes me think their whisperings had something to do with me is because one of the girls look at me first. After that, she would whisper something to her female friend. And most of the time, they know I can see them doing that. But what does it mean when they do that?
Why does it mean when a girl whisper something to her female friend right in front of me?
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