A knife is a nautral right-the foundation of modern man, even dna is cut with a knife:)
Had a friend who left a shell in one of his hunting jackets accidentily, besides being harranged at the airport he got a letter from HS saying he was on a list and if anything came up in the future they would go after him (paraphrase),
I'm sure Bush would have rendered him for waterboarding if he had been caught with a knife
Have never been confident the letter openers actually pass through undetected
