Upon standing still for a second, the Demon Hunter regenerates 3% of his/her maximum Life per second. This can stack up to 3 times, for a total of 9% of maximum Life per second, but it will fade away 5 seconds after movement.
Brooding is a Demon Hunter passive skill, unlocked at level 25.
The mechanics of this skill function as follows: the skill generates a stack every 1 second spent without movement, and all accumulated stacks are lost if the character moves for 5 consecutive seconds. If the character moves for less than 5 seconds and then stops for at least 0.5 seconds, the accumulated stacks are not lost.