If screeners cannot yet identify something that really is not suspicious (whatever that means), and with their wild imagination they think they see something that may go boom, why not just ask the passenger what they may have in that bag?
After the passenger explains to the screener what may appear as an item that may go boom, maybe the screener then can make sense of what they are seeing.
I also think the boys are anxious to play with all their toys that our tax dollars have bought to fight terrorism. With no real bombs ever found, the stuff just sits around collecting dust. I think they get really giddy when they have a chance to break out all the neat stuff at their disposal.