This trait makes mobs run in fear allowing us to hit them without being hit for a short time. Maybe a version of cry of the predator for non-animals. It is a great solo combat skill.

To get it ou must acquire the book at the AH (always more than 1G) or get to level 39 and get it randomly from other level 39+ humanoids.

Talk to Legolas to get the quest (other legendary trits can be bought or farmed).

First 4 pages are dropped by wights at Nan Tornaeth (Trollshaws). You will have better chance to get the pages drop if you go there by dawn or evening. During the day you may get lucky but there are more wights during night.
- While doing this you will get reputation items for elves and some good looting that you can sell.

The other 4 pages drop from dwarves at Gabilizan (Misty Mountains).
- The dwarves drop some interesting items and the plus that there are crates and ancient vases for scholars.