She held tightly to his arm to reassure him that he was in no danger.

"It's a train. A subway train. It runs on tracks that go underground. It will take us to our destination much faster than if we tried to travel by car. This way there are no lights to stop at and no traffic to worry about." She tugged him back a little so that people exiting the train would have room.

"We let the people off, then we get on. When we get to the station we want, we get off. Just like riding a horse, only it's a machine."