The hell hound is pure black with red eyes. You didnt say the eye color so i'm assuming its not that.. maybe a spirit of a past pet of yours, or a familiar, or possibly a shadow
My dog just kinda stopped and looked at it. Today when I was walking my dog she kept stopping to turn around and look at something and when I looked I swear I could feel it back there. I feel I should mention this isn't the first time I've seen them, When I was a kid I lived in Glastonbury Ct and behind my house was a forest that ran into a swamp. I used to to love playing and running barefoot through the forest and swamp, and I used to see them all the time and at night they'd hang out around the houses in our naighborhood. I stopped seeing them after we moved to NC and its been about eight years and now they've started showing up again.
Some more information, they don't like direct light I have seen them during the day but only when it's overcast and only in the forest and swamp. They only seem to enter populated areas at night. One more thing, I have seen one of them in NC before, it was before we moved to a different part of NC. By our apartment was a dirt road that led to a transfomer station in the woods. I was walking down it at dusk and was about to come to the station when I look up and about 10 in front of me one of them is just standing there like it was waiting. I stop walking and just stare at it when it rises up and it dosen't look like a animal anymore, now it looks like a person. Then it just vanishs like the others. We moved a few months later, that was a about 4 years ago. This is the first time I've told anyone about this or wrote it down but now that I have I'm starting to see a pattern and I feel like that's not a good thing.
I have seen these things near swampy forests and the like before, too.
It is my belief that they are often an aspect of the forest; nature spirits that are generally harmless. Like wild animals, they may appear aggressive or otherwise alarming. Treat them with respect and be cautious, as you would with any wild animal.