I've played Shadow in front of several friends over the years and it's funny how they react to the geyser of "blood" that comes from each stab of your sword. Aside from the fact that the Colossus are imposing and wield earth shattering cudgels, there's really no other graphical, extreme violence in the game. I'd argue this was for the purpose, like many other elements of the game, of emphasis, but you'd have to extensively play the game to get the supposed effect, which doesn't explain the immediate reactions. The high-pressure geyser of blood is pretty eye-widening even without context.
Maybe it's just culture shock, since the effect is distinctly Japanese.