Your sister has nicknamed you "Happy". It's so cute! It comes from her hearing is say "that baby happy" or "that baby not happy" when you are crying. I can't get her to pose in pictures with you or hold you yet. She's still so young at 2 and she loves you, but I think she still doesn't completely understand you yet. However, she adores you and if she doesn't see you in the mornings after I get her up, will run around the house saying "Happy happy" until she finds you!