Article from the Aiken Standard

You don't get a name like cottonmouth without the chops to back it up. With its cotton-white mouth, the snake attempts to make itself look as large and fearsome as possible, like many animals. "They will give a threat display," said Dr. Whit Gibbons, ecologist at the Savannah River Ecology Laboratory.

As with all of South Carolina's venomous snakes, the cottonmouth, or water moccasin, is not overtly aggressive. However, it will stand its ground and bite if it feels a grave threat. Adult snakes are generally a dark gray, olive or brown in color. A cross-banding pattern may be seen, especially on the sides. Adult cottonmouths are fairly thick and usually between three and four feet long, but snakes as large as six feet have been recorded. The young snakes are more distinctly patterned, resembling a dark copperhead without the reddish tint. A distinctive attribute of this snake are the pits between the eyes and the nostrils.

Gibbons said a keen eye should be able to identify these pits from several feet away. These heat-sensing pits consist of two cavities separated by a membrane. They are able to detect temperature differences of as little as 1.8 degrees Fahrenheit higher or lower than that of the background. They allow the snakes to strike very accurately at the source of heat - often a bird or mammal that is potential prey.