Wife was stopped by Japanese security inspectors as we were checking in for a flight from Tokyo to Sapporo. They found a 4- or 5-inch folding knife in a neglected pocket of her daypack. We were shocked - she had been traveling with that daypack for at least a year, had gone through TSA screenings at multiple US airports, some international airports too. The knife had a ceramic blade, but it was a BIG knife (ceramic knives are popular in Japan - in fact, we had bought that knife in Tokyo on a previous trip). She had stuffed it in her day pack to take to work one day long before (great for slicing fruit, she said) and had lost track of it. Oops.
The Japanese security staff were, of course, incredibly polite and surprisingly sweet. They asked us to please stop, then presented (showed) us the knife with a deep bow, apologized for the inconvenience, and told us the flight crew would give the knife back to us upon landing in Sapporo. Oh, Japan - please never change.
Yes, the suggestion to check all pockets for forgotten items before you start packing is good advice. Apparently it's quite common for US TSA agents to find loaded guns on people going through screening. Hmmm.