Train Conductor

I consider train conductors to have the most mysterious job in the world. They travel all over the country taking tickets and dispensing travel information, and they hang out in tucked away sub-basements of train stations playing cards and watching old TVs. Most mysterious about their jobs is how they remember whose tickets they've taken and whose they haven't. At each station a new group of straphangers climbs onto the train while others get out. I know the conductors use pieces of paper tucked into the backs of seats to keep track of whose tickets they've taken, but it's not like people take those things with them when they get off the train. It's a sloppy system at best. But still, not one conductor has ever walked past me and not asked for a ticket, nor has one ever come by and asked for my ticket twice. And I can't decipher how they're able to do it.