Answer:
   
   There is a law in the Torah that a childless widow who wants to marry
   her brother-in-law ought to marry him (a "leverite" marriage, or in
   Hebrew "yibum"). The child would then be named after the first
   husband. If either she or the brother refuses, they perform a ceremony
   called chalitzah, which involves his taking off his shoe and her
   spitting in it and saying "This is what is done to someone who won't
   carry on his brother's name." The definition of shoe for this law is
   quite rigorous, and the court generally has a ceremonial shoe set
   aside that fits this definition.
   
   However, no one does yibum anymore. The feeling is that modern man is
   too likely to be interested in this as quasi-incest and not enough for
   loftier motives for this to be the proper choice. In the western
   communities, chalitzah has been the preferred choice since the 10th
   century. In Sepharadic communities, and those from Moslem countries,
   it has been the choice for a little over a century or so.