When you die and go into ghoul form, a new action bar comes up.
Some of the options are: auto attack. claw and explode
When you click explode, you have a 1.5 second cast and deal 25% of your maximum health to anyone around you. Explode - Spell - World of Warcraft
When you are casting explode you can spam auto attack and claw for some extra damage.
This is an exploit because you shouldn't be able to use abilities while casting.