On June 22, 2021, manga artist Nerno Daiski flipped over his sneakers and plucked out some pebbles that were stuck in the grooves of the soles. But rather than just throw them away, which he thought "was a waste," he decided to start collecting them. And from that day on, using a toothpick as a tool, he carefully cleaned out the debris wedged in his shoes. After a year, he has neatly curated all of the found items into a display of 212 pieces (see images below), which includes "179 pebbles, 32 pieces of glass" and "1 nut," according to a translation of his tweet.
At this point, he says he's become really interested in the difference between the goodies found in the left versus the right shoe, according to an interview on nlab.itmedia.co.jp, and plans to continue collecting, but perhaps with a new, interesting approach that he's still mulling over.