Girls, Why do you make a fake cough?

When it's just me and a girl "never talk with her" in the lift for example, I just keep very calm and let the time go till I go, but the girl make a fake cough or little bit noise, what does that mean? Is it annoying or weird to be calm that way? This situation happen to me several times with different girls
Girls, Why do you make a fake cough?
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