Can someone really be someone else’s slave?

This is the last question in another guise. Is it possible for there to be consensual non-consensuality? That is, can someone agree to be in a situation from which they cannot escape, and to live that way?

This topic can inspire flame wars, as follows: historical slavery was totally non-consensual and enforced by the state; at the worst of times, the life of a slave was in the master’s hands. Our society today does not recognize such an arrangement. Does this mean that someone cannot truly become someone else’s slave, as society would always permit the slave to back out? Or is true slavery possible as a bond between one person and another, regardless of society? You expect an answer in a FAQ? Sorry, here there are only more questions. (Though see another question for more on the hazards of that pesky word “real”.)