Gorefiend tightened his fist and blood suddenly burst from the hapless orc’s nose, eyes, and mouth. Gorefiend had already turned away by this point, having lost interest in tormenting the annoyance. “Dark magic!” one of the Shadowmoon warriors shouted, grabbing up the axe beside him. “Kill the warlocks before they can afflict any more of us!” he bellowed, and his fellows responded by readying themselves as well.”[1]
Warlocks have the ability to siphon life from their victims. This ability appears to have been used by the warlock-death knight Teron Gorefiend to torment a member of the Shadowmoon clan.
In the RPG[]
This section contains information from the Warcraft RPG which is considered non-canon.
Gouts of blood erupt from a victim's eyes, nose and mouth. The streams spin and twist into a single, larger, rope-like stream as they bridge the gap between the target and the caster. The caster opens his mouth and draws in the stream, gaining vitality as the victim weakens.[2]
Patch changes[]
Patch 3.1.0 (2009-04-14): The Siphon Life spell has been removed. [Siphon Life] now causes your Corruption spell to instantly heal you for 40% of the damage done.
Patch 3.1.0 (2009-04-14): The Siphon Life spell has been removed. 
[Siphon Life] now causes your Corruption spell to instantly heal you for 40% of the damage done. 
[Shadow Mastery]. 
