Calling someone dead takes courage. It's not enough to cock your head, screw up your nose and say "Are you dead?" or "I think you're dead." You cannot expect an opponent to hang their head in shame and say, "Yes, I am." No one is obligated to declare herself dead, nor should she be.
If you look at the photograph above (sorry for the fuzzy focus) you will see four seven cracks and three greens exposed. Is she dead? What do you think?
To confidently make a death call you first need to know what hand is being played. Could there be more than one possibility? Rose has three seven cracks and three greens exposed. Hmm...look at the card. Only one hand it could be. What tiles does she need? A pair, maybe? A pair of what? Oh, I know. Seven dots. Are they out? Let me look at the table. Ooo, there's two out. Agh, I have one. What should I do? If I throw it she may mahj. If she doesn't mahj, she's dead. If I keep it, I can't mahj. Aaaagghhh.... You throw the seven dot. You've killed her. No one says anything. Rose frowns almost imperceptibly, but then stays poker-faced. Myrna picks. Myrna throws. Rose is dead. You know she's dead. She knows she's dead. Maybe Myrna and Shirley know, but they aren't acting like they know.. Wait, you think. Is she really dead? Yes, she is. Maybe there's another hand? There's no other hand. Okay, just say it.
"You're dead. Three seven dots are out."
This would be the time for Rose to admit defeat and cease playing. If she doesn't and merely scoffs at your accusation, insisting her hand has every possibility of being a winner, then you must play till the end and if she can't prove you wrong, she must pay you $.25.
Now, about those jokers. There is much confusion about taking jokers from a dead hand. After all, the hand is dead, right? Shouldn't the jokers be dead, too? The answer is no...and the answer is yes.
If her exposures contained jokers before the hand went dead, then, yes, those jokers can be taken.
But if the exposure caused her hand to go dead then, no, they can't be taken. In fact, the League recommends that an exposure that causes a hand to go dead should be returned to the rack so there is no confusion. In the hand above, if there were jokers in those exposures they would still be good, because they were good at the time they were exposed. In other words, the hand is dead, but the jokers are still alive, wiggling and shimmering and screaming "take me, take me." A dead hand is like a body you step over on the battlefield. The soldier is dead, but you can still take his gun and boots and move ahead to victory.