Your friend suddenly asks, "Did anything go wrong on the trip?" — answer honestly and naturally, even if you hadn't planned to mention a problem.
Your friend asks, "How was that different from [Destination] you visited before?" — you have to compare two trips on the spot.
Your friend asks, "Would you go back? Why or why not?" — give a real opinion with a reason, not just yes/no.
Your friend says, "Wait, back up — tell me more about [something you just mentioned]." — expand on a detail you only briefly mentioned.