SCREEN AND ASSOCIATED EQUIPMENT HAD PLUGGED WITH WET PRODUCT. OPERATOR SHUT SYSTEM DOWN AND PROCEEDED TO CLEAN OUT SHUT. HE PODDED OUT SHUT AND USED A SLEDGE HAMMER ON THE OUTSIDE OF CHUTE. AT ONE POINT HE FELT A PAIN IN STOMACH. PAIN PASSED QUIKLY AND HE KEPT WORKING. OPERATOR NOTICED A LUMP ON THE STOMACH THE NEXT DAY.