Riddle

Back online again! So, firstly, why is it dangerous to have a nap in a railway carriage?

Too easy? Then how about this one?

Secondly, what is the difference between a person late for the train and a school-mistress?

1st: Because the train always runs over sleepers.

2nd: One misses the train, the other trains the misses.

^{Source: “A Thousand and One Riddles, With a Few Thrown in”, Victorian book published by George Routledge and Sons Limited, London.}