Looks like Haji is feeling empowered since he has learned he can make the deer scatter.
It reminds me of when I first introduced city-dog Elijah Blue to rural living. He, too, was empowered when he learned he could scare cows. (Not to worry, JB had a come-to-Jesus meeting with him shortly thereafter and the cow chasing was nipped in the bud.)
As far as Haji chasing deer, he'll never catch them. But in the meantime, maybe he'll end up saving some of my plants.