That looks like a black rat snake. They often "kink" their bodies when predators/humans approach. Other signs; long, thin body. Black on top and white underneath (note: cottonmouths can be almost black on top and very light brown underneath).
Here are some pictures I found to help you.
Cottonmouth - note the stout body:
Black Rat Snake (harmless) long, thin body; smaller, thinner head:
Cottonmouth:
Black Rat Snake (harmless) much longer in proportion to their girth:
Cottonmouth Head - vertical pupils:
Black Rat Snake Head (harmless) - round pupils, different head shape and markings: