It's wisest. Things can go wrong at any stage in an operation, and plan B may not fit circumstance X.
(dismissive; less taken aback by this prospect than by the stickness of the stick he gave Hagrid himself) You wouldn't have been able to excuse that as in the spirit of the exercise. A diagram, yes. If you study on your own, you'll be doing it from books, so you need to be able to interpret them. So: show me what you did.
That's because our mother tongue is the sort that mugs other languages in dark alleys and rifles through their pockets for change. But most spells are not, in fact, in English.
Which kind of letters does it have more of?
Might be pretending not to have kept his casting up in case the law's watching, you mean?