His doctors pronounced him "the luckiest guy ever," and Patrick Lawler, 23, isn't about to disagree. The construction worker was building a house in Colorado when his nail gun backfired, driving a 4-in. nail through the roof of his mouth and into his skull. Amazingly, Lawler didn't realize anything was amiss until six days later when he went to a dentist with what he thought was a nagging toothache. It took surgeons four hours to extract the nail, which had penetrated his brain. The uninsured Lawler is expected to make a full recovery but now must contend with the headache of a $100,000 medical bill.