Girls, Why is one of her friends suddenly noticing me?

I like this girl at my work I certainly can feel something has been going on between us. Recently one of her female friends has started talking to me and acknowledging me. Like I've never ever made an effort with her friend before and neither has her friend made an effort with me. Suddenly her friend is talking to me out of the blue, her friend has made some eye contact with me and just acknowledging me in general.
Girls, Why is one of her friends suddenly noticing me?
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