Through the mechanical grinding action of weather and tides (the same mechanisms that make sand out of rock and coral), these chunks can become much much smaller, small enough to cross the intestine into the bloodstream and small enough to cross the blood brain barrier or pass up your nose, lodging in your brain.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10141840/
https://jamanetwork.com/journals/jamanetworkopen/fullarticle...