Snake-stone

A snake-stone, also known as a viper's stone, snake's pearl, black stone, serpent-stone, or nagamani is an animal bone or stone used as folk medicine for snake bite in Africa, South America, India and Asia.
The early Celtic era European Adder stone is also called a snake stone, and is usually made from coloured glass, often with holes. Its purpose is for protection against evil spirits rather than snake bite.
The World Health Organization is very clear in stating that it has no effect on snake-bites, bearing in mind that most snake-bites are from non-venomous snakes.They state that traditional medicines and other treatments such as wound incision or excision, suction, or application of “black stones” should be avoided. 
Descriptions.
Accounts differ widely on how to make and use a 'black stone'.
In Peru, a black stone is a small charred cow bone "applied to the site of a poisonous snakebite and tied firmly in place. It is left there for several days, during which time it supposedly draws the venom from the wound."
Persian/Iranian writer Kazwini describes the snake-stone as being the size of a small nut. An injury inflicted by a venomous creature is to be immersed in warm water or sour milk. The snake-stone is then dropped into the liquid to supposedly draw out the poison.
Although called a 'stone' in the Congo, a black stone is often made from animal bones. When taken from snakes, it is usually from the head, but also said to be extracted from the tail.
The steps suggested in an African leaflet are:
Views on snake-stones expressed in scientific studies.
A Nigerian study recommended "education on the need to avoid the use of popular first aid measures of doubtful benefit." The same doctors later reported that black stones may be beneficial, but "those who used the black stone required significantly higher quantity of antivenom as compared to those that used the tourniquet". In their report they noted slightly higher tissue necrosis in patients who use tourniquets, but this was not (statistically) significant; other scientists have recommended against tourniquets (see "treatment of snakebites" and "outdated treatments").
A Bolivian medical study stated: "contrary to widespread belief, no efficacy to treat envenomation may be expected of the BS" (black stone).
An Indian study stated: "unscientific methods like 'black stone' healing contribute to the delay in seeking appropriate medical care."