Whenever I visit my sister, Kate, in Delray Beach, Fl., I usually take a stroll along the seashore and flip small clam shells over with my big toe before bending down to pick one up. If the shell doesn’t have a small, perfectly round and neatly drilled hole through the hinge area I leave it be.

I look for pre-drilled shells to make into whistle necklaces. Some are colored with bands of browns, golds and charcoal grays. The solid black shells are fossilized and ten thousand years old. All of them are very hard and nearly impossible to break using bare hands.

The holes in the clam shells are drilled by rapacious moon snails. Each snail can eat many clams per week. They use their file-like tongue and acid to drill the hole before injecting digestive enzymes that dissolve the clam. Then they suck the liquefied meal out through the hole and move on to their next victim.

One day I was walking along the beach collecting shells. A lone person was kneeling in the sand several yards below the wrack line. She was wearing gray sweat pants, a long sleeve gray sweat shirt, sneakers and dark sun glasses. She appeared to be about my age and was filling an empty plastic soda bottle with small clam shells. I walked by and said “hi”. She didn’t answer me or even look up. This bothered me for some reason, so I turned around, walked back and knelt down on the sand right in front of her.

Before she had time to react I said ” clam shells make really loud whistles” and picked one up from the sand. I held it between both thumbs, brought my thumbs to my lips and let loose a startlingly loud, high-pitched whistle. She said “you must be whistling with your mouth and I don’t believe the clam shell made the whistle”. So I showed her how to do it. A few minutes later I stood up and continued my walk.

As I was leaving the beach I heard a distant whistle. I turned to see her standing, with one arm raised in a triumphant salute. She whistled again and waved at me. I waved back, whistled with my clam shell and left the beach smiling.