Sometimes, when I'm proctoring an exam, I end up with a little too much time on my hands. So I play with stuff—whatever I've got on hand. In this case, it was one of those clicky pens. It had stopped writing, so I assumed it was out of ink. Of course it might not be out of ink, so I took it apart to look at the ink cartridge and check. That's when I discovered the fun stuff: If I push the empty ink cartridge down into the top of the pen, it compresses a spring.

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