When flying recently, I was slightly concerned after when my carry on bag was selected for extra scrutiny after going through the X-ray machine; the culprit: cheese. I was bringing back four bars of 1 ¾" × 1 ¾" × 6" cheese I haven't been able to find in California. My bag also had some batteries and electronics in it. The cheese packaging was swabbed and analyzed and I went on my way. I thought this was a little silly, but I moderated my view when I was catching up on back issues of Science News during the flight and read an article that said
cheese and plastic explosives can look the same under X rays. The new and improved X-ray system being discussed will be able to tell apart C4 and four cheese!