Why does my coworker repeat what I say?

I have a female coworker…who repeats what I say…in her normal voice not a mocking one. She used to do this, stopped but has repicked up the habit. I think out loud so I tend to walk and talk…and I noticed she repeats what I say when I’m thinking out loud. Also when I’m bored I make random noises which she also repeats. It doesn’t bother me if anything it makes me laugh and smile… because I just hear this small echo in the distance. Just curious as to the cause of the habit?
Why does my coworker repeat what I say?
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