There’s a reason they call it a “belly laugh”: Laughter is a bona fide stomach flattener! “Laughing tones a group of stomach muscles called transverse abdominus. That’s crucial, because most forms of exercise can’t isolate these muscles, which are key to having a flat, toned belly,” says Chicago-based certified trainer, Stephanie Mansour. For a slimmer, sexier stomach, Mansour recommends a