Can You Find the Disturbing Detail In This Photo?

I was browsing Imgur when I saw a challenge — someone posted a picture with the title, “It took me forever to find out what’s wrong here.” So naturally, being someone who can’t find the glasses on top of her head, I thought I was qualified to try and figure it out. Below is the picture in question. First of all, I thought maybe it was that the girl on the left somehow threw out her back from that pose, but nope that wasn’t it. Your hint is that you have to try and at least make eye contact once. Source: Twentytwowords