Complex sentence: Most species of rattlesnakes can control how much venom to inject and have hemotoxic venom, destroying tissue, causing necrosis and coagulopathy (disrupted blood clotting).
Split into simpler sentences: Most species of rattlesnakes can control how much venom to inject. The venom is hemotoxic, destroying tissue, causing necrosis and coagulopathy (disrupted blood clotting).