Many years ago I was on a business trip in the Netherlands. I was a speaker and when I finished I was given a small package by my host (whom I knew well).
I was in a hurry, so put the package into my bag and ran for the train to AMS. The bag went through the scanner at AMS and raised eyebrows.
The security agent asked me if I been given anything and I dutifully responded "yes". Seeing the look on her face, I continued "That was the wrong answer, wasn't it?" She burst out laughing and we opened the offending package, which turned out to be a lead-crystal paperweight (the lead blocking the X-rays in the scanner).