But you know how when all else fails the government likes to charge people with telling a lie. "No" is too absolute. I think "Not that I know of" means No, but leaves wiggle room later when the TSO who thinks he found the Big Catch™ finds a Walkman and bag of peanut butter and cheese that looks like a b*mb on his x-ray. Or if you are that one in 5 billion where TheBadGuy managed to slip a package into your bag when you were not looking.

/paranoia.