Larry, all snakes have teeth. The rows of teeth in a Gray (or Black) Rat Snake will look like fangs. A Water Moccasin, or Cottonmouth, is a snake of swamps, and does not approach this size. Also, a Cottonmouth has a completely different pattern. Almost all snakes have a white inner lining of the mouth, making them look like a Cottonmouth when alarmed; the Black Rat Snake I caught Tuesday showed a white lining to the mouth while biting me three times (she was very frightened), plus, when looking in the Peterson's Guide, it doesn't look like Cottonmouths make it to Northern Alabama. Of course, people will call me a liar, and say they have seen "Water Moccasins", but these are simply Water Snakes, and are harmless.

Probably an Eastern Garter Snake ... their color varies wildly, but the black head and stripes along the body with sort of "checkerboard" patterns between the stripes is one variant. They are not venomous, but they will bite and also release a VERY SMELLY fluid if you handle them. http://www.paherps.com/herps/snakes/garter_snake/

Garter snake. Not venomous, eats slugs and other things. Don't try to handle them - they can secrete a very smelly substance to make predators go away.

I just wrote out a big long answer discussing things like Racers, Watersnakes and Black Rats discussing the pros and cons of each......and then it occurred to me what it actually is! This is a melanistic (black) Eastern Gartersnake (Thamnophis sirtalis). The melanistic (black or black-backed) morph is common in some areas in the north of the species range.