My theory: they aren't looking for paper, they are trying to rule it out as something else. My understanding of these scanners is that they colour-code "organi

My theory: they aren't looking for paper, they are trying to rule it out as something else. My understanding of these scanners is that they colour-code "organic" and "inorganic" material differently. Explosives generally show up as organic. Now, if you have a block of such organic material in just the right position next to some electronics, the conveyor gets stopped and you will be taken to one side and asked some very direct questions about the contents of your bag. I know this because I once had a protein bar in the same bag as a portable DVD player and that aisle went into lockdown for about 30 minutes because it looked exactly like a bomb, from all angles, in 3D. Expert called over, agreed they couldn't start the conveyor until they knew it was safe. My guess is that paper (in the form of small pads) is the commonest cause of this type of false positive.