• Discerning Eye of the Beast
• Item Level 1Disenchants into:
  Not disenchantable
• Binds to Battle.net account
• Trinket
• +64 Intellect
• Requires Level 1 to 80
• Equip: Restores 2% of your maximum mana whenever you kill a target that yields experience or honor.

Source

This item is sold by the following vendors for 2,725 :

•  Enchanter Isian <Heirloom Vendor> in Dalaran
•  Enchanter Erodin <Heirloom Vendor> in Dalaran
•  Brammold Deepmine <Antiques & Heirlooms> in Dalaran

• also from  Dame Evniki Kapsalis <Crusader's Quartermaster> in Icecrown for 75 (requires <Crusader>)

Notes

The 2% mana restore on killing blow stacks with other Discerning Eye of the Beasts. For example, if you have 2 of these trinkets you'll receive 4% of your total mana back per killing blow. This effect does NOT have an internal cooldown, unlike similar trinkets.

This item refers to the [Eye of the Beast], a possible quest reward, involving killing General Drakkisath in Upper Blackrock Spire.

Patch changes

• Patch 3.2.0 (04-Aug-2009): Dame Evniki Kapsalis added. 
  
•  Hotfix (2009-04-21): "The heirloom item, Discerning Eye of the Beast, will now return mana at any level. ^[1]"
  

References

External links

• Battle.net (EU)
• Wowhead
• Thottbot
• WoWDB