As Oberon wonders whether Titania has woken and with whom or what she's fallen in love, Puck enters and tells Oberon that Titania has fallen in love with a monster. He explains how he saw the laborers, transformed Bottom's head into the head of an ass, and then "Titania waked and straightway loved an ass" (3.2.35). Oberon is pleased.
But just as Oberon asks about Puck's success with the Athenian youth and Puck says he used the potion as Oberon asked, Demetrius and Hermia enter, fighting. Hermia suspects Demetrius has harmed Lysander because she doesn't believe he would abandon her. Demetrius insists he didn't hurt Lysander, but Hermia nonetheless tells Demetrius to never enter her presence again, and exits. Demetrius decides not to follow because she's so angry. Soon, he falls asleep.
The scene between Demetrius and Helena, is here reversed, with Hermia abusing Demetrius. Imbalances of love create imbalances of power.
Oberon realizes what has happened and scolds Puck: "What hast though done? Thou hast mistaken quite / and laid the love juice on some true-love's sight" (3.2.91). He orders Puck to search the forest for Helena, and use some illusion to bring her to Oberon, who will make Demetrius fall in love with her. Puck exits.
Oberon sees that the "play" he's trying to write in which everyone's happy isn't working out, and sends Puck to set it right. The lovers, though, don't know they're being manipulated, so to them this play is like a dream.
Oberon puts the love ointment on Demetrius' eyes as Puck returns with the warning that Helena is on her way and trailed by the lovelorn Lysander. Puck is excited to watch the two men woo Helena, saying, "Shall we their fond pageant see? Lord what fools these mortals be" (3.2.117).
Helena enters with Lysander following and begging her to see that his vows of love are authentic. She doesn't believe him. Just then, Demetrius awakens, sees Helena, and falls in love. When he professes his love, she is furious. She thinks that now both men are mocking her.
The two men now begin to fight and argue over Helena, and each tries to get the other to settle for Hermia.
Love can cause strife between men...
As Demetrius and Lysander argue, Hermia enters. She demands to know why Lysander abandoned her. Lysander tells her it was love that made him leave; his love for Helena. Hermia can't believe what Lysander is telling her. Meanwhile, Helena now thinks that Hermia has joined with Demetrius and Lysander to mock her. She calls Hermia an "ungrateful maid" (3.2.200) for turning on her now after their long friendship and for joining with men in mocking a fellow woman.
…and it can lead to strife between women as well. Love is celebrated as a great unifier, a creator of intimacy, but it can also rip friends apart.
Hermia can't understand why Helena would accuse her of such a thing. She demands Lysander tell her what's going on. But Lysander tells her to leave him alone and says he hates her. Hermia realizes Lysander is serious, and turns on Helena. She calls her "a thief of love" (3.2.297). Helena, who still thinks Hermia is making fun of her, responds by calling Hermia a shameless puppet, implying that Hermia is faking her emotion. But Hermia, who's shorter than Helena, thinks Helena is making fun of her height and claims "I am not yet so low But that my nails can reach unto thine eyes" (3.2.312-313).
And love can expose a person's greatest insecurities. Just as her failure in love earlier convinced Helena she was not pretty, now it begins to eat at Hermia, who fears she is too short.
Helena asks Lysander and Demetrius to protect her, which they gladly do, though she never ceases to think they're mocking her. The rivalry between the men, though, has grown so fierce that they leave the women alone and go into the woods to duel for Helena's love. Helena, frightened of Hermia, turns and runs. Hermia follows in hot pursuit.
And beyond emotional pain, love can cause physical pain. Through this fight between Lysander, Demetrius, Hermia, and Helena, Midsummer shows nearly every aspect of the destructive side of love.
Oberon suspects Puck of having intentionally caused this mayhem. Puck swears he made an honest mistake, though he adds that he's glad he made it. Oberon instructs Puck to keep the men apart with illusions and tricks. Puck does just that as Oberon exits to go get the changeling from Titania.
And through it all the fairies are the audience for the mortals antics. And not just an audience, but writers too: Oberon sends out Puck to "rewrite" the mistakes that resulted in this play that the lovers don't know they've been caught in.