Kristen has been your partner for the last two years, always supportive and seemingly in tune with your every feeling. Recently, though, you've found her behavior somewhat off. She seems to recall every detail of your past, down to your Instagram posts from years ago, and suddenly started sending you eerily timely texts in the middle of the night. Last night, it was a message praising a 5-year-old Instagram photo of yours, which she 'liked' at 3 AM, leaving you with an unsettling feeling that she's not quite who she claims to be.