Of all things living...

a brother's the worst.

Well, maybe not the worst. Slugs are fairly vile. Having older brothers can be such a trial.... They never let up. When you're young... they tie you up when they're supposed to be baby-sitting you. *Cough Adam Cough* Then, they tie you up and hang your arms from a doorknob. *Cough Adam Cough* Then, they pick you up and threaten to throw you over the banister on the second floor. *Cough Adam Cough* Then, they get older and think they know everything from the airspeed velocity of an unladen swallow to the bolting speed of a slobbering hell-hound.

Observe (from Adam) :

I'm going to see if I can get you wound up further...he he he.

You said the hellhound looks like a doberman that you fed a cow to everyday.

You said it looked like a doberman would to a mouse.

You said it was Honor's height.

Let's say that the hellhound is five feet tall. Not incredibly large. Certainly couldn't eat a cow. Sure it could gnaw on the cow but it wouldn't eat a whole cow. Could probably kill one though.

A regular doberman is 27 inches tall and about a hundred pounds.

Assuming the same build, a five foot tall doberman would weigh around 1100 pounds. It actually would need to be much thicker in order to hold up its greater weight so the same proportions wouldn't hold. Probably closer to 1500 pounds or more.
An eight foot doberman would weigh around 4500 pounds. Again, proportions would probably need to change so it might be 4 or 5 tons.

A five foot doberman would have a stride length of more than twice that of a regular doberman. A regular doberman can probably run 30-35 mph if pressed. If a five foot tall doberman could move its legs as fast as its smaller version it would be running a blistering 65-75 mph. Most likely its greater mass would slow it significantly but there is a reason why Usain Bolt is the fastest man. He has got a wicked long stride. I can't see a 2 foot doberman outracing a 5 foot tall doberman unless the five foot tall doberman was not meant for speed. Something tells me that hellhounds are supposed to be pretty fast to keep their prey from escaping.

Either that or they need to be able to whisk in and out of hell to catch their victims no matter where they might run to or hide.

I'm sure you've done many of these calculations. I just wanted to keep you awake tonight. he he he.