In Season 4 Episode 7 "Mockingbird" of Game of Thrones, we are reintroduced to "the Mountain", Gregor Clegane, an almost literal mountain of a man. He was summoned to King's Landing by Cersei to be her Champion against Tyrion in Trial by Combat. When she (i.e. we) greets the Mountain, he's busy introducing his sword to some people's insides.
But who were those 'soon to be dead' men? Prisoners of war? Criminals in King's Landing? Unlucky squires in training? People who owe the Mountain gambling money? Random low-born citizens?
Why was the Mountain making mole hills out of these men?