This requires the talent
Reaping - Spell - World of Warcraft
Use blood strike or blood boil to make ONE Blood rune used and made a death rune. Immediately after use Blood Tap and your 2nd blood rune will be a death rune for a long time. It seems to randomly reset, but works for a long time as said above.
this rune will also refresh as a death rune until it randomly resets.
simple guide:
1. Hit bloodboil or bloodstrike once.
2. hit blood tap
3. profit.
Working as I type this.
by Acry