The elements of the Eucharist, sacramental bread (leavened or unleavened) and sacramental wine (or by some grape juice), are consecrated on an altar (or a communion table) and consumed thereafter. Communicants, those who consume the elements, may speak of "receiving the Eucharist", as well as "celebrating the Eucharist". Christians generally recognize a special presence of Christ in this rite, though they differ about exactly how, where, and when Christ is present. While all agree that there is no perceptible change in the elements, Roman Catholics believe that their substances actually become the body and blood of Christ (transubstantiation). Lutherans believe the true body and blood of Christ are really present "in, with, and under" the forms of the bread and wine (sacramental union). Reformed Christians believe in a real spiritual presence of Christ in the Eucharist. Others, such as the Plymouth Brethren and the Christadelphians, take the act to be only a symbolic reenactment of the Last Supper and a memorial.