Annoyed or weird habit?

I've had a cold lately, so I've been really congested. Whenever I sniff my nose, my friend looks at me and then sniffs hers too. It's really weird. At first I thought she was trying to subtly hint that my sniffing is annoying, but she's been doing it so often that I feel like it's uncontrollable. I've been really congested, so this has been happening SO often that I'm convinced she doesn't realize she's doing it. She even did it last night when I heard my other friend sniff. I'll simply be reading or on my computer, sniff my nose quietly to myself, and out of the corner of my eye, I see her glance up, then sniff her nose too. I'm so confused. I'm not really sure how habits like this work. Any answers are greatly appreciated!