We were once shown a video of a large bull getting hit by a taser. It dropped the bull cold and instantly. After the taser cycled, the bull got up so angry that he full-force charged the steel fence that the operator was standing behind. That must have hurt. It shows how angry that bull must have been.

The taser is designed to penetrate thick layers of clothing, so I have to believe that the needles could find their way through thick hair. I don't see a problem with that. If you ever saw the barbs that come out, you would understand.

One problem is the effective range. One would need nerves of steel to wait as long as you would need to and still maintain good sight picture. At that range, there would no chance of a re-load.

The biggest problem, over-riding all other variables, is that the animal is only incapacitated for a very short while. Even if your shot is good and the barbs penetrate, you only have seconds before, as Yamamoto said, you awaken the giant with a terrible resolve. Unless you had solid protection very close by, you will wind up with a bigger problem than before.