The mechanicals are rehearsing the play in the forest. They think of problems with the play, and Nick comes up with humorous ideas to solve them.
You thief of love!
Stop mocking me, you little...
Puck watches the rehearsal and decides to play a prank on Nick Bottom. He turns Nick's head into a donkey's, and when Nick goes to perform his part, he is confused why the other mechanicals are running from him.
Put the antidote into Lysander's eye.
To try to bring the other mechanicals back, Nick sings and wakes up Titania, who falls in love with him at first sight and instructs her servants to tend him.
Helena and Hermia have a big fight because Helena feels mocked by the other three and Hermia is furious at Helena for stealing her love.
LITTLE!!! Do you think I'm so little and low when I claw your eyes out?
Oberon orders Puck to lure the Athenians to sleep, and gives him the antidote for the love-in-idleness flower. Puck puts the antidote's sap into Lysander's eye.
Hermia arrives and doesn't understand why Lysander says he doesn't love her anymore; she is shocked when he harshly tells her that he never loved her, but loves Helena.