Levirate Marriage and Halitza
The institution known as Levirate Marriage (called Yibum in Hebrew) requires that a man marry the childless widow of his brother to produce a child who will carry the deceased brother's name, so that the deceased brother's name will not be forgotten. Levirate marriage is detailed in the Book of Deuteronomy (25:5ff), "If brothers dwell together, and one of them shall die and have no child, the widow shall not be married to another man who is not his [her husband's] kin. Her husbands brother shall come unto her [have intercourse with her], and take her to him as a wife, and perform the duty of a husband's brother unto her. And it shall be that the firstborn that she bears shall carry the name of the brother that died so that his name not be blotted out of Israel.”
If the brother of the deceased refuses to marry the widow Deuteronomy (25:7-10) explains that the wife then must go to the gate of the city where the Elders sit, and inform them that her brother-in-law has refused to marry her. The Elders then must call the brother to them, and if he states, “I will not marry her,” the ceremony of the Removed Sandal (halitza) takes place. In this ceremony the widow loosens or removes the brother-in-law's shoe, spits in front of his face, and says, “So shall be done to a man who refuses to build up his brother's house.” Only after this symbolic act is the widow free to marry who she likes. Today, only the Orthodox continue to require that halitza be performed.
Source: Kolatch, Alfred J. The Jewish Book of Why/The Second Jewish Book of Why. NY: Jonathan David Publishers, 1989.