It's written that these strings contain only letters.

Yep, I came to the comments after looking at the question and example and wondering... what do they want?

replacing anything that's not 'aeiou' with nothing and returning the length of the string

nice! pretty clear.

Are there not some standards for describing problems?

After reading the problem and pondering for a few minutes, I immediately came to discussion to see if there was any good discussion on articulating the problem more clearly.

My primary issue with the write up is that there are 'leaps' between each of the sections, and it's not clear what the leaps are because of the way the problem is organized.

Basically, I felt dumber for reading the problem. And now that I understand the problem, I didn't have an 'aha epiphany'. I had an epiphany that the problem is poorly constructed.

It took me forver to realize that the O in moOse was not a 0 (zero). I might suggest for future test that the character is ambiguous and may confuse someone (as it did me). I was left wondering why on earth my code was passing and then it hit me after 10 minutes... it is a capital 'o', not a 'zero'. The words 'otTer' or 'lettEr' or 'meMory' might be more apparent.

Because it doesn't need to test against itself. And it no longer needs to be compared once it's been tested.