Stay alert. If you cross paths with this dog, he might morph into his true form, and eat you. The best thing to do would be to carry a bazooka with you at all times, just so you have some hope of surviving an encounter with this foul creature.
WHAT EXACTLY IS THIS "DOG" REALLY?
This "dog" is actually a Hellgremlin. These gremlins are rare, extremely powerful, and date back thousands of years. In their true form, they are extremely hideous, and thrive off of eating human blood smeared inside of Peanut butter and jelly sandwiches. Lots of times, the Hellgremlin will use its mind control abilities to force it's victims to make the very PB&Js that their blood will later be smeared in before killing them.
Hellgremlins are extremely intelligent, and very proficient in the use of firearms, and they are also very good with martial arts, so don't engage in direct combat with them. Use crossbows, RPGs, rifles, or any other weapon that gives you a good amount of distance to take them out.
Good luck folks, and good hunting. The future of humankind depends on you. Remember, that cute little puppy you got for Christmas might actually be a Hellgremlin waiting for you to go to sleep so he can transform, assrape you, shit on you, and then chop you up with a hacksaw and eat you in a sammich. You can't be too trusting.