How can you tell if a snake is venomous?

There is no way to tell just by looking at a snake whether it is venomous or not. You can't necessarily tell a venomous snake by its verticial slit pupils and triangular-shaped head. There are many harmless snakes who share these properties with venomous ones (the slit pupils indicate a night-hunter); and the coral snake, which produces a potent nerve venom, has round pupils and a bullet-shaped head.

Snake, Venomous Snake, verticial Slit Pupils, Triangular-shaped Head, Round pupils