"Smart cookie," he says appreciatively. "So you're on this boat, and you're halfway across the water, and allll of a sudden who could it be on the loudspeakers but your friend the Joker. Who tells you that your boat is rigged to explode, and - ha! - so's the one with all the criminals on it! And it just so happens that he has left you each a present, to wit, the detonator for the other - boat. Annnnd, naturally, whichever boat hits the button first wins the race and gets to live, whereas if you both wait around past midnight, or if anybody tries to escape, well, he's got detonators too."