Generally there are two types of snake; one that kills by using venom produced by their body, and the other using sheer strength to strangle their prey to death.
Anaconda, for example, is a constrictor. They have teeth that points backward to provide an even tighter grip on the victim. Once bitten, they would immediately wrap themselves around their prey. Once imprisoned in the embrace of death, it is very unlikely for the prey to escape.
A constrictor tightens its constriction every time the prey exhale, and with every breath the prey takes, it becomes harder to breathe. And finally you cant even expand your chest to breathe at all, and you die from suffocation.
Note that constrictors do not have venomous fangs. They rely purely on their muscle strength and stealth. Like their venomous counterpart, they also have infrared or heat detection pit near their mouth to help detect the body heat of their prey.
Apart from that, they also have a weapon in their tongue. The tongue is sensitive enough to detect the most minute change in chemical content of their environment.
How to differentiate a venomous snake and a nonvenomous snake?
Ans: by looking at the shape of their head. Venomous snakes usually have a triangular-shaped head, meaning it's wider at the neck and narrower at the mouth. Nonvenomous snakes have a rather round-shaped head, which provides a firmer grip and more room more muscle.
Apart from that, venomous snakes are usually smaller in size. The largest venomous snake, the King Cobra, is merely 3 meters in length. In the contrary, constrictors such as the Anaconda and Reticulated Python could grow up to 30 feet long(approximately 10 meters).
Constrictors grow to that length because they need enormous muscle and lengthy body to constrict their victims(It's not easy to constrict a deer you see....), while venomous snakes tackle smaller, faster mammals such as rats and squirrels. They do not need huge muscle mass as the venom could do the job for them.
The King Cobra, the largest venomous snake in the world, is hailed as god in India, despite hundreds of people being bitten by the species every year. One drop of King Cobra venom could kill up to 160 people.
The most venomous snake in the world, the sea snake, lives in waters off Indonesia and Sulawesi, though they can be found in other parts of the world too, mostly in the Pacific and Indian Ocean. They are relatively small, and their venom is almost 100 times more lethal than any other snakes. The reason why their venom is so potent is because they hunt fish for food.
And unlike land animals, fish could get away really fast. Land snakes can track their bitten prey through scent, but fish doesn't leave scent trails for sea snakes, so the sea snake need a venom potent enough to paralyze their victims before the prey gets too far.
Snakes are equipped with complicated senses to look out for their prey even in the darkest night. Once bitten, the venom would start to digest the prey from within.
There are four distinct types of venom; namely neurotoxin, hemotoxin, cytotoxin, and also proteolytic venom.
Each reacts differently based on the type of prey the snake consume.
But they all kill.
The only way to treat a snake bite is by using antivenom.
To produce antivenom, we need the venom from the snake.
First the snake will be milked, ie you often see in documentaries where the snake is forced to bite on a plastic sheet to release its venom into the jar. Then the yellowish venom would be diluted and injected into a large mammals' body, normally a horse. A horse immune system would develop antibody to counter the venom in say, two weeks time. Then the horse will undergo blood transfusion to draw out the blood, and within the blood lies the precious antibody we call antivenom to treat snake bite.
Unfortunately, snakes are threatened by extinction too. Snake skin is used to make bags and leather products, and there are also demands for snake bladder from the Chinese black market, as it believed that it could enhance their blood circulation.
Although baby snakes are equipped with the essential survival tool i.e venom and muscle, they are easy meal for birds and mongoose. Survival rate of young snakes is very low.
Religion, too is playing a part in the snakes' demise. In the bible, the snake is linked with the devil, and early missionaries condemned the worship of snake in India, and that eroded the protection of snake as well.
We should do something before this wonderful creature follows the path of other extincted animals. Some religious fanatics kill thousands of snake every year to justify the teachings of bible. If the bible encourages things like this, ie pushing animals towards extinction, then I think the bible should be revised and rewritten.