GREY'S ANATOMY - "Walk on Water" - Beginning February 8, Grey's Anatomy enters a three-episode story arc that will challenge the interns of Seattle Grace -- and "Grey's" fans as well -- like never before. "Walk on Water" airs THURSDAY, FEBRUARY 8 (9:00-10:00 p.m., ET) on the ABC Television Network. Elizabeth Reaser (Independent Spirit Award winner for "Sweet Land") guest stars as a patient over multiple episodes. (ABC/VIVIAN ZINK) KATHERINE HEIGL, ELLEN POMPEO, SANDRA OH