A magician sends a Jinn to the targeted woman and instructs him to cause her to bleed, To do so, the Jinn enters the woman's body and circulates in her veins and arteries with the blood,, This notion of circulation has long been warned about by the Prophet (PBUH) in the following tradition:
Satan circulates in man's body like blood (Al-Bukhari: {Fath Al-Bari: 4/282) and Muslim (An-Nawawi: 14/155)
When the Jinn reaches a known vein in the woman's womb, he stomps it so that the vein bleeds This fact was also pointed out by the Prophet (PBUH) when Hamna bint Jahsh asked his opinion on the issue of bleeding outside the period of menses, and he (PBUH) said:
Such bleeding is but one of Satan's stomping. According to At-Tirmidhi, the above tradition is sound and authentic, according to Al-Bukhari, it is sound
According to another tradition:
The bleeding is the result of Satan's stomping on a vein rather than from a normal menses. Imam Ahmad and An-Nasai (a very good chain of transmission)