Courtesy National Zoo The National Zoo announced way back in April that “Happy,” its 28-year-old Nile hippopotamus, would be leaving this year and moving to the Milwaukee County Zoo in Wisconsin. Well this morning we received word that Happy sneaked off in the dead of night on Monday and is already in Wisconsin, arriving at about 3 a.m. this morning. Did we mean so little to you, Happy, that you had to run away…