Here's a short story:

At three a.m., Jack Mills was sitting at the controls of the mail train. The train was made up of 13 cars. At the end of the train, 71 mailmen sat sorting the mails. Inside the second car, there were only five mailmen and 128 bags full of five-pound notes. This train had run more than 100 years without being robbed. At three minutes past three, Mills and his helper, David Whitby, saw a yellow warning light. They slowed the train, and then stopped. Whitby went to the telephone beside the track. It was out of order. Then he saw a man moving between the second and the third cars. Before Whitby could give a warning, he was knocked down by two men. Mills' cars with all the mailmen had been disconnected by the robbers. At the bridge, the bags of money were unloaded from the train and thrown into waiting trucks. One of the robbers who obviously knew the schedules of all the trains kept looking at his watch. At 3:45 he said, "That will have to be enough." The robbers drove away with more than 2,500,000 pounds. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: What time does the tale commence?
Guess: 3:00 AM

Question: Who's driving the train?
Guess: Jack Mills

Question: At what time does his helper see the yellow light?
Guess: 3:03 AM

Question: What did they do next?
Guess: slowed down

Question: At what time does his helper see the yellow light?
Guess: 3:03 AM

Question: Did they train stop after slowing down?
Guess: Yes

Question: Who saw the yellow light?
Guess: Mills and Whitby

Question: What happened at the bridge?
Guess: bags of money were unloaded

Question: How much did the robbers get away with?
Guess: more than 2,500,000 pounds

Question: At what time did they stop before making their getaway?
Guess: 3:45

Question: How many mailmen were in the second car?
Guess: five

Now answer the following question in the same format.

Question: What were the bags full of?

five-pound notes