A head of genetically modified broccoli shrieked its numerous benefits at shoppers Monday in a Seattle-area Safeway. 'I contain 40 percent more vitamin A than non-modified broccoli!' the head screeched at terrified produce-aisle customers. 'I can fight off insects and disease without the use of pesticides!' Monsanto, makers of the vegetable, stressed that genetic-modification technology is still in its infancy, and that more pleasantly voiced broccoli should hit store shelves by 2003. 