WHAT IS THIS??

i do appreciate the quick reply, i thought it was sand, but why would there be so much in there? Was it just not cleaned well during casting? the engine ran but i am assuming this could make it run warmer than it should?, any way to run a filter to catch what i may have missed? or is it just stuck in there? sorry for all the questions i just dont want any issues going forward once i get this cleaned up and plugged.
Poor quality control