In the dream of the mare, young Raskolnikov sees a drunken peasant beat a mare to death with a whip in front of a laughing crowd, and the boy's gesture, which embraces and kisses the dead animal's muzzle, reveals in him a compassion that predates the theory, which the crime later silences.
The dream comes in Chapter V of Part One, on Petrovsky Island, after he has wandered through the islands of the Neva. In the dream, he is seven years old and walks with his father on the way to the cemetery, where his grandmother and a little brother who died are buried. At the door of a tavern, the peasant Mikolka harnesses a thin mare to a heavy cart, calls everyone to climb aboard, and when she cannot pull it, beats her with the whip, with the cart's pole, and finally with an iron bar. Voices in the crowd shout that he has no cross on his chest. The boy runs among the adults, is pulled back by his father, who says it is a drunkards' affair, and then "embraces her muzzle, dead, bloodied, and kisses it, kisses it in the eyes, on the lips."
On waking, Raskolnikov tells himself what the plan would require: "Is it really possible that I will take the ax and begin to strike the head?" He renounces it and feels "free of these enchantments." Hours later, at Sennaya Square, he hears the hour at which Lizaveta will leave the old woman alone, and the next day he strikes the pawnbroker "almost without effort."
The scene returns throughout the book. When Katerina Ivanovna dies, her last cry is "They've worn out the old mare!" In another dream, it is Raskolnikov who beats, and the victim laughs. The boy's gesture also reappears in kisses: on Sonia's foot, on his mother's feet, on the earth of the square. There are two readings of the dream: a warning from conscience that rebels against the plan, or the memory of a pain he learned to keep silent.