What is the sure sign of intestinal obstruction

Vomiting may or may not occur at the outset but becomes conspicuous and bile-stained with time. Initially, the passage of stool may be normal, whereas, later, blood and mucus are evacuated - the 'redcurrant jelly' stool.Classically, the abdomen is not initially distended; a lump that hardens on palpation may be discerned but this is present in only 60% of cases Ref: Bailey & Love&;s Sho Practice of Surgery,E25,Page-1194