Mental reading is no worry since you don't have to breath. 
That's one of the main reasons why you shouldn't worry.

Edit:
You are filling the sentence with dead space.

For instance:
"The boatbuilders' blood stained the snows as we fell upon them, leaving their cold bodies behind as we stole their ships, for the endless winter has made us strong; our hearts are cold and some say that ice flows through our veins."

Cut it down a little and it would turn into:
"The boatbuilders' stained the snows as we fell upon them, leaving their bodies behind as we stole their ships.(, for the endless winter has made us strong.)"

But overall you shouldn't worry.