Apparently, to the TSA employee working the X-ray machine, this:
looks a lot like this:
One is a ceramic water filter, the other.. well. I think you can figure that one out. The TSA inspector did too. But if you're a hiker / backpacker, it's worth keeping in mind. Luckily the Billings, MT security check point is pretty quiet at 2pm on a Tuesday, and Montanans are pretty laid back.