I was on my war-steed on my hunter last night and occasionally, a mini tool bar would pop up with three buttons whose tool tips indicated they were to hurl a spear. The three different buttons were for different amounts of fury. I could not see a pattern to the appearance of the buttons though.

I had never seen these on my lore-master, nor have I seen anything in release notes about it. Can somebody clue me in? What triggers it? Is it stance dependent?