Which is usually followed by more of the same.
I have a rule, though, that he may not ask me "Why?" when I tell him to do (or not to do) something, because that becomes the forerunner for talking back. Instead, we practice saying, "OK, Mom" or "Yes, Mom". (Occasionally, after I have given him instructions, the "Why?" is a genuine question, and after he has given me the proper response, I will explain why.)
This morning, we had gone through the pattern three or four times already. I told him not to do something, he responded "Why?", and we went back to the beginning and talked through the appropriate responses. Finally, as he was completely absorbed with attempting to sharpen a colored pencil with his fingernails (slivers under the fingernails, anyone?) I told him to go put it away before he got hurt. He automatically responded, "Why?", and we started over.
"Let's try that again, Isaak. Go put the colored pencil where it belongs before you get hurt." I prompted him, "What do you say?"
Still intently inspecting the end of the pencil, he answered, "Thank you!".
At least something is sinking in!