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While holidaying on the Greek island of Paxos, I came upon a pebble beach where many of the stones had apparently been 鈥渆ngraved鈥� by some type of creature. This example (see photo) is roughly 50 by 60 millimetres, but the same sort of pattern was also present on much larger stones. What type of creature made these, and how and why?

Mick Groves, Oxhill, Warwickshire, UK

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This article appeared in print under the headline 鈥淩ock and hole鈥�