Paarthurnax can teach me one of three "deeper understandings" of th'um. Fus, Feim, and Yol.

Fus: You stagger 25% less, and stagger enemies 25% more often.
Yol: strengthens the power of the fire breath shout by 25%
Feim: ?

Nothing show's up in active effects. Anyone know what it does?

UPDATE- I just looked up the meaning of Feim, and it means "Fade" and is used in the "Become Ethereal" shout. I still don't know why it doesn't tell me what is effected.

Last I heard it made you heal more when in Ethereal Shout.

Ok, I'll check it out. I can't proceed until I make a decision because
This one seems the most interesting from the rest.

I don't think it's working. If you check your active effects, nothing shows up when you meditate on "Feim"