Search for the bodypart "Head", only that part can have a skill :
A Ghoulish Head for the skills Rush Attack + Fatality
A Goblin Head for Fireball
&
A Dragon Elf Head for Magic Missile + Magic Blast

I order of rang, from below to the highest level :
Rotten(1), Infested(2), Damaged(3), Slightly Damaged(4), Preserved(5), Well-Preserved(6), Clean(7), Clean-cut(8), Fresh(9) & Perfect(10).
So this "(number)" is corresponding also with the level of the skill on the Head (for example: a Preserved Goblin Head has Fireball level 5).

There's something strange too (for me): the Wisdom skill, on Goblin Heads I believe, but always Wisdom 0 (zero) ! Why ?

On 7th of february 2015 : I start a new adventure in the Divinity world of Original Sin,
it's a Fantastic Freaking Fabulous Funny ... it's my All Time Favorite One !