In the sentence fragment "...a, again, subnormal woman..." is "an" better than "a" because of the vowel starting "again"? This is choosing "an" based on sound rather than grammar because the "a" is associated with the "subnormal woman".
My thinking is that "an" is actually correct -- but the problem easily goes away by rewriting the fragment as, for example, "a subnormal (again) woman".
It really is all about the sound:
<< The deciding factor for which of these words [a or an] should be used is the sound that begins the word which follows these indefinite articles, rather than the letter which does. And there are scads of words in English that begin with a vowel, but which are initially voiced with a consonant sound (and vice versa).
One, useless, unicorn all clearly begin with a vowel; yet one sounds as though one is saying W, and the other two are voiced with an initial Y sound, and so these would be preceded by a, rather than an (“A one hundred dollar bill”). On the flip side, we have plenty of words that begin with consonants, but which are voiced as though they begin with a vowel (especially for H-words, such as heir, honesty, hourly), and these words are preceded by an, even though they begin with a consonant (“He was an honest man”). >>
https://www.merriam-webster.com/words-at-play/is-it-a-or-an
When you make a vowel sound like "a", your mouth is open... so it's easy to transition to a consonant (which generally involves obstructing the flow of air). Going from an open mouth to a consonant sound is generally easy to do.
When you say the word "an", the final sound is the consonant n. You make an /n/ sound by putting the tip of your tongue against the roof of your mouth. This makes it easy to transition to a a vowel sound.
Try saying "a cat" and then saying "an apple", and take note of your tongue placement. The N really does move the tongue!
Given all that, I would go with "an, again, subnormal woman."
