Because it feels so good to stop.

R: "I'm sorry, Mom! I'm sorry! I'M SORRYYY!"
Me: "Go calm down in your room. Dale, why is Rachel screaming?"
D: "She went like this [squeezes his cheeks hard] to me." (We would call that scratching because squishing your face is too long.)
Me: "Why did she do that?"
D: "I was going to tell that she scratched me."
Me: "Why did she scratch you?"
D: "Because I was going to tell on her."
Me: "What did she do that you were going to tell on her?"
D: "She scratched me."
Me: "You were going to tell on her for scratching and so she scratched you?[Affirmative nod.] How many times did she scratch?"
D: "Once."

My head hurts.