One explanation is that it was a Hitlerism ..he said in 1930...
"If our movement is victorious there will be a revolutionary tribunal which will punish the crimes of November 1918. Then decapitated heads will roll in the sand."
Although it can be applied generally to any decapitation ..and we are famed for chopping off peoples heads !
It just an idiom which means people will be in deep trouble if something they should have done correctly goes wrong... with dire repercussions !