Mother opens on its title character, alone in a grassy field. She stops, looks around, sways a bit. Is she about to faint? No, dance. Lifting her arms, she begins to sway gently in the breeze: hips wiggle, arms wave. Mother is happy.As for the rest of us, we're intrigued. As well we should be: Mother is a an artful and a mesmerizing murder mystery from Korean writer- director Bong Joon-ho (Memories of Murder, The Host). You never know where “Mother’’ is going to go next. All you know is that you’re in the hands of a master with an appreciably bent sense of humor.