"Seashell", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License
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This is roughly equivalent to 'number of times I've picked up a seashell at the ocean' / 'number of times I've picked up a seashell', which in my case is pretty close to 1, and gets much closer if we're considering only times I didn't put it to my ear.