Faer Gorta are skeletons animated using necromantic magic. These are mindless creatures possessed only of their combat instincts and a dislike of living beings.
There are several different kinds of Faer Gorta:
Faer Gorta have no weaknesses, and all four kinds are immune to both poison and bleeding1.
When performing a stealth kill on a Faer Gorta, the death sound that is triggered is that of a male human, and is not heard by the Faer Gorta at any other time.
Despite their skeletal appearance and their apparent lack of any circulatory system, Faer Gorta can bleed and can suffer Bleeding damage2.
1Tested multiple times on all four kinds of Gorta with bows (with components *always* causing bleeding and poison on a charged shot when possible), there was never any damage or animation shown except the initial arrow impact. Unless there's a condition or clarification that wasn't mentioned (only bleeding damage from potions, which I didn't test, or only in an earlier patch, which I also won't test, or only certain abilities or animations but not damage, etc), then 2 is incorrect. Leaving the base text intact for an easy fix if more information is brought forth or if somehow my eyes and ears lied to me.