Titania, Queen of the Fairies, has a spell cast over her by her husband Oberon, making her fall in love with the next "thing" she sees. Unfortunately, the man bottom has been enchanted and given an ass's head, and he is the first item Titania sees upon awakening. (painting: Fuseli's "Titania and Bottom" courtesy artmagick.com)
In the play within the play, Shakespeare features the Thisbe and Pyramus romance. The scene is based on the ancient story about Thisbe and Pyramus whose parents forbid them seeing each other. They exchanged wedding vows through a crack in the wall between their gardens. The painting here is JW Waterhouse's "Thisbe" (courtesy of artmagick.com).