Lola, a 2-year-old Siamese cat of generous proportions, likes to graze all day long. "She weighs 12 pounds!" said Alison Lewis, her owner. Until the discovery last month of the country's first case of mad cow disease, Lewis thought more about how much she fed Lola than what she was feeding her. For the first time, standing in the pet-food aisle of a Queen Anne grocery the other day, Lewis studied the ingredient list on the bag of fish-flavored dry food Lola prefers. "There's lots of stuff that looks really nasty," she said. "What exactly is animal digest? And beef...