Quick answer
Read the two exposed sets for the handful of card lines they fit, then name the tiles those lines still need. Those are the hot tiles, so hold them and discard tiles none of the candidate lines can use. A tile that player has already discarded is usually safe. If you are four or more tiles from mahjong, stop chasing your hand and play for a wall game.
Two exposed sets on one rack changes the hand for everyone. That player has told the table most of what they are building, and the tiles that finish them are now knowable. Here is how to read the two exposures, how to find a safe discard, and how to decide whether your own hand is still worth chasing.
Read what the two exposures say
Every exposed set is a pung, kong or quint, so the hand is an exposed hand, not a concealed one, and it comes from a section of the card where those sets appear. Two exposures rule out every section that cannot hold both sets. Matching numbers across suits fit Like Numbers, a pair of even pungs fits 2468, and a pung of dragons beside a numbered set fits whichever sections pair them.
Look at the card with those sets in front of you and find the handful of lines they fit. You do not need to know which line exactly. You need the family, because the family tells you which tiles the player is still hunting.
Count what they still need
A hand is fourteen tiles. Two exposures account for six to ten of them, so the player is holding four to eight more, and nearly every line needs a pair somewhere. What is left to find is one or two more sets plus that pair, and each candidate line names them.
If the missing pieces are all pungs and kongs, jokers finish them and the player can be closer than the rack looks. If a line needs a natural pair, no joker can fill it, so those tiles have to be real, and a discard can be called for that pair only when it wins the hand.
Name the hot tiles
The hot tiles are the ones the candidate lines still need. That means the same number in the missing suit for a Like Numbers hand, the remaining evens or odds for a numbers hand, the dragon that matches an exposed suit, and the flowers or winds a line calls for. Say them to yourself before you discard, every turn, until the hand ends.
Then check the table. A hot tile with three copies already out has cooled, because nobody can want the last copy for a pair. It can still fill a set built with jokers, so it is cooler, not safe. Any hot tile nobody has seen is the one to fear.
Find your safe tiles
A safe tile is one the candidate lines have no use for. That means a suit and number none of them needs, or a wind or dragon that fits none of the sections in play. A tile with three of its four copies already visible is a good candidate too. Only one is left and a joker can never be part of a pair, so nobody can want that tile for a pair. It could still fill a set built with jokers or stand as a single.
Discards the player has already thrown are usually safe too, because they let that tile go once, which says their hand had no use for it then. Usually, not always. A hand that changed direction after a joker exchange is the exception.
Decide whether to keep attacking
If you are two or three tiles from mahjong, keep going, but throw the safest of your own spare tiles first and hold the hot ones until you have no choice. If you are four or more away, the hand is now a defensive one. The aim is to reach a wall game or let someone else feed the winner, not to finish.
East discards first every hand, which means East hands the table information before anyone else has acted, so a player sitting East with two exposures has been readable since the first discard. East carries no payment bonus, though. The doubling in American scoring comes from how the hand was won, not from the seat.
When to break your own hand
The moment your only remaining discards are hot tiles, break the hand. Throw a tile from your own keep set that is safe by the count above, even though it costs you the hand. Paying for someone else's mahjong costs more than a wall game, and it costs everyone else at the table too.
Breaking a decent hand costs you a hand you might have won. Feeding a better one costs you that hand and a payment as well.
The tells that they are one away
A player who stops rearranging their rack, who discards without thinking, or who starts watching one particular suit go by may be waiting on a single tile. So may a player who exchanged for a joker two turns ago and has been silent since.
Reading exposures is the skill that makes those tells useful, because the tell says when and the exposures say what. Defend the Table in the Drill Room gives you a real hand in progress against exposed sets and grades each throw with the reason it is safe or not.
Put it into practice
New to the game? Start the course at Lesson 1, Meet the Tiles. The first three lessons are free and need no account.
Already play? Have the coach read a real dealt hand for you, free. It names the direction the hand goes for, what to keep, what to pass, and the reasoning behind each call.
Defence means holding the whole count in your head while your own hand wants attention. Defend the Table in the Drill Room drills exactly that. You get a real hand in progress against exposed sets, one throw to make, and the reason each throw is safe or not. Visitors can try it free, and members get it without limit.