The stones can be as big as your fist. The method, says the attorney-general in Nigeria's Sokoto state, is up to the judge. "They will dig a pit, then they will put the convict in a way that she will not be able to escape, and then she will be stoned," says Aliyu Abubaker Sanyinna. "Another way is that she could be tied up against a tree or a pillar."
That, so far, has been the extent of the flexibility of the courts in northern Nigeria to the death sentence passed on Safiya Husseini. Her crime, if you can call it that, is sex outside of marriage. She calls it rape; the judiciary insists it was adultery. The evidence: the word of the father and her pregnant state. The punishment: under the most severe interpretation of sharia law - to be stoned to death in public. And the man concerned, who withdrew his confession to her parents and the police that he was the father, has now fled.
"It takes a man and a woman for there to be adultery," says the leader of a Nigerian-based women's rights organisation. "But only the woman is being punished, and she is being punished in a manner that is not in keeping with sharia law or the tenets of Islam."
Husseini, 35, was sentenced last June and, following one stay of execution, will have her appeal heard on Monday. Yakubu Abubakar, who is already married to two other women, comes from the same village of Tungar Tudu in north-west Nigeria.
"He said he loved me," says Husseini, a divorcee with two children. "He used fetishes and magic on several occasions. When I was in the bush one day he ambushed me and forced me. That happened three times. I found myself pregnant."
Rumour soon spread round the village and the police arrived not long after. Originally, says Husseini, Yakubu was to acknowledge the child and look after her until the birth. But when her father asked him to marry her, Yakubu's elder brother forbade it. And when it was clear what the repercussions might be, Yakubu bailed out. "I was taken to sharia court," says Husseini. "Yakubu said he had never met me. He denied everything and said he had never done anything to me. I had witnesses who heard him admit [it]. I don't know why they were not listened to."
Husseini could not deny everything because she already had Adama, who is now 11 months old. She did not say she had been raped in the first trial. And by this stage Yakubu had already bolted. "I felt like dying that day because of the injustice," says Husseini, who was originally sentenced to die as soon as she had finished weaning Adama. "Then the judge said I was guilty of adultery. When he passed sentence I broke down in tears. I never thought there would be such a penalty.
"It is because I am poor, my family is poor, and I am a woman. He [Yakubu] used his money to get away with it."
While Husseini's case is extreme, the concerns it raises for women in particular and the country in general are by no means unique. Last year a teenage single mother, who became pregnant after she says she was raped by three men, was given 100 lashes in public and then forced to marry one of several men who had presented themselves to her. The courts say she was 17; her parents say she was 14.
"The situation here is very fragile, particularly for women who are living alone or with their children," says the representative of one Nigerian women's rights organisation. "There are moral police who are going around looking for infractions and women who are living alone are upset because nobody knows who is watching you or what they might say about you."
According to a spokesman for the Nigerian High Commission in London, around nine of Nigeria's 36 states currently operate under sharia law. But while sharia has been customary in many of these areas for the best part of a century it used to run in tandem with the civil code and was never implemented with this degree of harshness.
Its recent resurgence in the north is the product of broader developments taking place in Nigeria which have little to do with religion. With the collapse of military rule under dictator Sani Abacha two years ago, and the introduction of democracy came the reemergence of longstanding tensions, particularly between the principally Muslim north and the non-Muslim (largely Christian and animist) south. In the north, politicians sought a popular rallying point against the endemic and prevailing corruption, widespread crime and state pillaging that had characterised Abacha's era and seized on the most severe version of sharia. Saudi Arabia and Sudan sent delegations to support Zamfara, the first state to adopt sharia, and donated large sums of money.
The result was an extreme, and somewhat sadistic, legal framework in some areas of the north and a sharp increase in ethnic tensions throughout the country. This has proved a serious embarrassment to the federal government on the international scene. "Some of our brothers in the northern part of the country have made so much politics out of sharia that it is denting the image of Nigeria," said justice minister Bola Ige, who is Christian, recently.
"The federal government wants the states to temper justice with mercy," says a spokesman from the Nigerian High Commission. "It will use all means at its disposal to ensure that the state takes notice of the international outcry and spares her [Husseini's] life."
The divisions have also thoroughly destabilised the country. Over the past two years around 4,000 people have died in clashes between Muslims and Christians in the north.
Earlier this month the region saw its first execution under sharia in recent times. Sani Yakubu Rodi was hanged for the murder of a woman and her two children. The authorities originally planned to stab him to death, using the identical method he had used during his crime.
His death - and the precedent it has set - makes those fighting for Husseini fear that the judiciary in northern areas may have be sufficiently emboldened to push ahead regardless of opposition.
There are four interpretations of Koranic law. The other three say the act of adultery must be observed by four male witnesses, or a conviction can be secured by a free confession. The Maliki interpretation, enforced in Sokoto, says pregnancy outside of wedlock is enough. Those campaigning for Husseini are not opposing the right of the states to impose sharia, which they believe would be a tactical mistake, but insisting that even within sharia the verdict is both flawed and exceptionally harsh.