When Alyosha comes out, Kolya gives him the back story on his relationship with Ilyusha. When Ilyusha first arrived at school, he was picked on by the kids. But Kolya appreciated his fighting spirit and defended him, and Ilyusha took to following Kolya around.
One day, Smerdyakov told Ilyusha that it would be really cool if he placed a pin in a piece of bread and gave it to a dog. This dog – the same Zhuchka that everyone's searching high and low for – eats the bread and runs off squealing in pain.
Filled with remorse, Ilyusha breaks down in tears before Kolya. Kolya isn't having any of that "sentimental slop" and sends Smurov to tell Ilyusha that he's breaking off their friendship for a short time.
Without Kolya's protection, Ilyusha is again pestered by the other kids, which led to the stabbing and stone throwing described in Book 4, Chapter 3.