In the mornings my beloved Blue Line Train is often temporarily stopped for what's called a security check. This check consists of a one of Chicago's Finest and a rent-a-cop walking the length of the train w/ a bomb-sniffing dog. I don't know about you but if I was a suicide bomber, I would be detonating my bomb just about the moment the bomb-sniffing dog pointed me out. Do you really think some guy who's itching to bomb civilians in downtown Chicago is going to worry about taking a cop w/ him? I'd think it practically be a bonus. I can hear them bragging in my head:

"Hey--guess what?--not only did I derail a train and kill couple thosand civilians, I blew the bomb right in that smug cop's face just as his fucking dog sniffed me out."