In this snippet, Roald Dahl is giving a list of reasons why his teacher Captain Hardcastle didn't like him, but not all of those reasons are equally likely.
- First, Dahl lists two reasons that were possible but not all that likely:
- that it was because Dahl was bad at Latin, or
- that he was almost as tall as Captain Hardcastle.
- Then he gives the reason he thinks is more likely:
- that Captain Hardcastle noticed Dahl sneering at his moustache.
Why not just give the most likely reason to start with?
Probably for dramatic effect: the first two reasons are reasonable but mundane; the third reason is more fanciful and funny. Dahl builds up to his punchline.