Last week, a couple's otherwise totally normal selfie went viral for the complete creepiness of the guy's girlfriend looking over his shoulder in the mirror. While that photo was simply the work of Photoshop, this week's viral brain bender is an optical illusion. On Monday, Twitter user @_ellebailey, 18, of Leeds, UK, posted a photo of her and her sister having fun with some friends in a nightclub. Seems pretty normal, right? Just a bunch of kids hanging out, except why is her sister's arm six feet long!? People were freaking out. But if you look closely, you realize she's actually a totally normal, human woman with regular-sized arms, and that the arm in question belongs to the girl on her left. That's what happens when everybody wears black!