In a mediation of a personal injury case, the plaintiff and…

In a mediation of a personal injury case, the plaintiff and defendant negotiate back and forth for over 10 hours about how much money the defendant is willing to pay and the plaintiff is willing to accept to settle the dispute. The plaintiff will not move off of $400,000. The defendant is stuck at $250,000. They both threaten to end the mediation.     What could the mediator do here to break the logjam?