I'm not sure what specific pattern this challenge is looking for, but it won't accept multiple valid patterns.
I started with
/[an]/gi which was rejected. (Full disclosure, I'm not watching the videos, since I am already very familiar with RegEx). So I checked the slides and it looks like it wants this form instead:
/a|n/gi but that, too, is rejected. I've tried just about every different configuration of those expressions (switching around modifiers, switching order of letters), and nothing is accepted, even though every expression grabs the same two or more characters from each word.
Interestingly enough, it did just accept
/[an].*[an]/ as the answer, which is actually incorrect since it also matches anything between the letters. The validation for this problem definitely needs to be reworked