<P> Transubstantiation ( in Latin , transsubstantiatio , in Greek μετουσίωσις metousiosis ) is , according to the teachings of the Catholic Church , the change of substance by which the bread and wine offered in the sacrifice of the sacrament of the Eucharist during the Mass , become , in reality , the body and blood of Jesus . </P>
when does the bread and wine become the body and blood
the sacrament of the Eucharist during the Mass