Cottonmouths an be quite aggressive. They will stand their ground against threats, and that, combined with a strong venom, can result in a nasty situation. They have even been known to approach humans. The mouth of a Cottonmouth can snap shut extremely fast, quickly injecting the venom. Their venom is hemotoxic, which means that it breaks down red blood cells, reduces the ability for blood to clot or coagulate, and causes hemorrhages.