What does “cause extra bleeding damage” actually mean?

Question

The Hack and Slash perk in the One-handed skill tree says that

Attacks with war axes cause extra bleeding damage

What is bleeding damage? Is it instant or damage over time? Do undead take bleeding damage?

I love the flavor of using war axes but I want to know more about this perk before I take it.

Answer 1

Bleeding damage is a damage-over-time effect: each rank in Hack and Slash will do one to two extra points of damage every second for a few seconds. It's essentially a fast-acting poison.

As in Morrowind and Oblivion, undead like skeletons are unaffected by poisons and effects like these.