It's an interesting question - and one with potentially many good answers! Our quibble of the week author Susanna Dodds seemingly notes a potential flaw in JK Rowling's magical world. Her essay points to the fact that a Boggart would probably have little to no effect on a person whose worst fear was falling or drowning.
For heights, supposing it would turn into a high building or a cliff edge, how is that going to scare you? Besides the fact that the building or cliff edge would be in miniature (proved by the fact that Professor Remus Lupin's boggart was a miniature full moon) you are clearly not standing on a high area so why would you be scared? Being afraid of heights doesn't mean you will be afraid of high areas if you aren't even on them. It may show you in miniature falling off a high area but again how would that scare you? You aren't really falling and you do not feel the sensation of falling.
What do you think - is Susanna correct that this is a flaw in the book series? Or would the Boggart have a different sort of effect on the recipient person than just changing its form? Leave your thoughts on this one in the comments below, and maybe we can all figure it out together.
Every week MuggleNet runs the Quibble of the Week challenge over in our Editorials section. If you would like your own Potter essay to be featured on MuggleNet, send an email to us at firstname.lastname@example.org.