Hi Sonia, to answer your first question, I think I need more information. What was the sentence that came before this one?
As for the second question, I would re-word it to "He smiled in response before launching into more thorough cross-examination." or "He smiled in response before launching into more cross-examining."
Also, it's better to say, "When someone says 'smile in response' in place of 'smile in reaction'?"