If you want to skip the back story, then read the next paragraph…
So a few months ago my family went to Atlantic City for a few days. I brought my yo-yo case, as usual. There we took a walk down the boardwalk, and I started yo-yoing. Eventually it came to the point where I had to change my string. I didn’t have my case, and thus my string cutter, with me at the time, so I had to struggle with a few inches of string dangling from the slipknot. Obviously this was a pain as the string kept getting in the way. So when we got to the beach, I looked down and found a broken clam shell. It had a rather sharp edge, so that got me thinking, “Maybe…”
It turns out that broken shells make good string cutters! You just have to rub the string back and forth against the sharp edge(s). Of course, shells don’t make the best, or easiest to use, string cutters (it takes a bit of work to cut the string and the shells dull over time), but they’re pretty handy if you find yourself in need of one in a beach. Just be careful not to cut yourself walking barefoot across the sand.