You are right, it should be fuil, an fhuil. The contributors know about it and it will get fixed but might take a while, the tips for the Animals skill state:
CORRECTION - Fuil (blood) is spelled with an accent on the 'u' in this skill, which is incorrect. We have earmarked it to be fixed, but that requires us to create a new version of the current tree. As soon as we are able to, we will change this. The pronunciation in the sound files is still correct. Thanks for your patience!