Walk. Run. 

He kept coming home sweaty. That was the first clue that something was amiss. But Melanie knew the way it worked: They don't come home sweaty from the tarts, they come home too soapy clean and groomed for the end of the day. That wasn't Donald. His Oxfords were soaked through. His slacks wet at the seat and crotch. Fat bulbs of sweat pimpled his forehead and temples before breaking apart to race each other down either side of his oblong eyes. Panting. Rubbery. Spent. Two weeks of it and Melanie finally confronted Donald only to be more confounded by his answer than she'd ever been by the symptoms. Her husband, it seems, had forgotten the difference between walking and running. A phobia? Ambulatory amnesia? No matter. Donald, sure that it would pass, refused to seek medical attention. He would simply wait it out, avoid situations likely to highlight the affliction, and buy new running shoes and track suits. After all, a man sprinting down the sidewalk in a business suit is outlandish. But a jogger is healthful, dedicated, honorable. And so Melanie became married to a health nut. He ate better. Took up yoga. In short, Donald became a dynamo. But as Donald made friends with his affliction, Melanie grew bored. He dropped 10 pounds the first month, but he was never home. They saved on gas, but between showers, re-hydration, and extra laundry, their water bill was absurd. Donald ran a marathon. Melanie took up smoking. Donald was promoted to Assistant Supervisor for Quadrant F. Melanie frequented the singles supermarket. It was six months into the illness, at the Quadrant F Christmas party, that Melanie began her flirtation with a punch press operator named Chuckie. He had enormous knuckles and displayed a flair for erotic euphemisms in their numerous chat-room trysts. And now, tonight, finally, it was time for Melanie to meet Chuckie alone. A small-town bar. Leather stools. He will goose her as she waits for the cigarettes to drop in the machine. In the morning, after the affair, all that will be left is the long, slow walk up her driveway in naked first light. Donald waiting in the kitchen. There will be an ugly pause, but Melanie already knows what she will say to break it. It starts with, "Because..."