As an internist at New York's Mount Sinai Hospital, Dr. Stephanie Santos is used to finding odd things in people's stomachs. So last spring when a young man, identifying himself as an Iraq-bound soldier, said he had accidentally swallowed a pen at the bus station, she believed him. That is, until she found a second pen. It read 1-800-GREYHOUND. Last summer, according to published reports, a 20-year-old Bronx soldier paid a hit man $500 to shoot him in the knee on the day he was scheduled to return to Iraq. The year before that, a 24-year-old specialist from Washington state escaped a second tour of duty, according to his sister, by strapping on a backpack full of tools and leaping off the roof of his house, injuring his spine.