Ok, it's no question that this ability rarely activates.. but I have came across something interesting:

I was mining around Treespeak today. I was doing leves and also hitting 3 specific mining nodes between leves. One of the nodes I was hitting was very interesting. Every time I hit this node, Sweat of Brow activated after the first hit.

I thought this may just be a fluke after the first two times it activated, so I just let it be. To my surprise, it activated again on my 3rd run-through. Same thing on the 4th. So I just did my 5th run through and it activated again.

So I am trying to find out other people's theories about this ability...because this was either a very bizarre occurrence or it has some kind of link to the way this ability activates.

Any thoughts?