Ever taken the Tube in London and heard someone announce "code six" - or, more intriguingly "Inspector Sands" over the tannoy?
Well, we have - and we were curious - so we spoke to some underground workers to find out what the codes mean.
We ran the master list past a TfL press officer who confirmed the codes were accurate, but we do have to include a word of caution - while Inspector Sands is the same in all stations, codes 1-6 are cleaning codes which are not uniform in every single station.
Here they are:
Code 1: Blood
Code 2: Urine/Feces
Code 3: Vomit
Code 4: Spillage
Code 5: Broken glass
Code 6: Litter
Code 7: Anything not fitting these categories (the mind boggles)
Inspector Sands: A fire alarm has been operated and staff have two minutes to come to the control room - if they don't check it automatically evacuates the station.
Now we know - and knowing is half the battle.