What particular episodes in "Hamlet" focus on the use of poison?
Several episodes focus on poison in "Hamlet."
On the literal level, there are three episodes involving poison.
In the first, Hamlet's father tells how he was poisoned.
In the second, the players put on a scene written by Hamlet in which a man poisons his brother, thus confirming Claudius' guilt.
In the final battle scene, there is poison in a cup and on the sword.
In addition, there is the suggestion of metaphorical or symbolic poison. Think of Hamlet's line early in the play: "Something is rotten in the state of Denmark."
Sin is poison here.
There are two episodes which include the use of poison. The first occurs when the ghost tells Hamlet how he was killed. He says he was asleep in his garden when Claudius poured poison in his ear. This caused his blood to curdle and he died. The last episode occurs at the end of the play. When Claudius and Laertes are plotting the death of Hamlet, Laertes says he has brought back some poison from France. A person only needs a small dose of it, administered by a cut or scratch, in order to be die. In the last scene of the play, Laertes poisons Hamlet in this manner but he also ends up poisoning himself. Claudius also has planned to poison Hamlet by putting it in his wine. Unfortunately, he ends up poisoning Gertrude and finally Hamlet gives some of the poison to the dying Claudius.