GREY'S ANATOMY - "Haunt You Every Day" - It's Halloween, and the day is full of surprises for the doctors of Seattle Grace - Alex receives an unexpected and welcome visit from his former patient, Ava/Rebecca, Meredith is convinced that her mother's ashes are haunting her, Cristina is snubbed by a surgeon she admires, and Callie announces George and Izzie's affair to their fellow doctors, on "Grey's Anatomy," THURSDAY, OCTOBER 25 (9:00-10:02 p.m., ET) on the ABC Television Network. (ABC/RON TOM) ELLEN POMPEO, SANDRA OH