I must confess to an incident whilst visiting the White House (no, I'm not that important - just the normal public tour). After passing through the X-Ray I was asked whether I had a pair of scissors in my bag. I replied negatively and the woman behind me was promptly surrounded by Secret Service agents and it wasn't until much later that I discovered that my first aid kit included a pair or scissors. I also tend to carry unusual objects in my hand baggage, and I can usually guess what item security pull me over for - with security it is rarely a random check; there is usually some item they cannot identify on the X-Ray.