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Its the bearings that usually go, the large end of the rod that attches to the crank has bearings betwwen its and the crank. These shatter\wear out and so the rod rattles about on the crank....
Also the big end journals on the crank get damaged as there's no proper bearing surface and it drags bits of of the broken bearing around itself getting hot and bothered.
Just to add..Keep running it like that, what's left of the shell may melt onto the crank journal, spinning the bearing in the big end. Keep going after that and your conrod will snap and most likely fly out the engine block.