Venomous Snakes

Venomous snakes are well, venomous. Other than strangulation being one of their USPs, they can even inject you with toxins capable of putting a person in paralysis, amputating the bitten body part, extreme pain and prolonged agony, and even death.

What makes them worse is their mastery in camouflaging making them practically impossible to spot in any environment. So you wouldn't want to step on one of these and bring upon your own death.