Ch. 4: What did Johnny do to Bob and what did he use? Describe Johnny's explanation of why he committed such an act. Where/how was this scene foreshadowed from a previous chapter?

Johnny stabbed Bob with his switchblade.

"You really killed him, huh, Johnny?"
"Yeah." His voice quavered slightly. "I had to. They were drowning you, Pony. They might have killed you. And they had a blade... they were gonna beat me up...."

This scene is foreshadowed by Johnny's previous altercation and violent beating by the Socs.