When returning from their burglary at Klaus' mansion, Michael and his two new school friends can be seen sitting in a subway whose cars are openly connected so that you can walk the whole subway from one end to the other without passing a door (which is a newer model of "U-Bahn"-trains in Berlin). When the three boys leave the train at the station, the subway model suddenly has changed. The type of cars you can see from the outside then cannot be walked continuously from one end of the train to the other. Instead those (older) cars are separate units connected "one by one" externally - to get to another car you would have to leave through the side doors and enter the next car the same way.