Reading opponent discards.
A discard is a public statement. The same card dropped by a player with one visible meld means something different from the same card dropped by a player at the bottom of the table. This long read walks through the four-discard read as the minimum work for credible inference.
The first discard is the loudest
On turn one, every player has just picked up their thirteenth card. The first discard tells the table what the player is most willing to let go of, which in turn tells the table what the player is most unwilling to let go of. A first discard of a 2♣ is the standard "drop a low card because I have no club work" signal; a first discard of a J♥ is the standard "drop a high card with no heart work" signal.
By table position
A first discard from the player to the dealer's left is the cleanest information, because that player has had the longest to read the table. A first discard from the player to the dealer's right is the noisiest, because that player has had the shortest read window.
The four-discard read
The four-discard read is the minimum work for credible inference: at every fourth discard, the reader stops play one turn and reconstructs the four most recent discards, mapping them against visible melds.
The four-card hand
If a player discards a 5♠, then a 6♠, then a 7♠, then an 8♠, the player has likely picked up the matching run earlier (5-6-7-8) — and either declared, used the run in a meld, or kept the run intact in the hand. The signal "this player does not need spades" is the table's working assumption.
The cross-card denial
If the player drops the discard needed for the reader's own meld, the reader picks up the closed-deck card instead. The denial costs the reader a turn but conserves the meld for the next hand.
Discipline: what to ignore
A reader's discard reading must ignore: friendly discards to mask a hand, deliberate discards to set a trap, and discards where the player is forced to drop deadwood to meet the turn clock. The four-discard read is best applied to a player who has not declared and is playing a standard tempo.