This is a video of the fun loving folks of Youtube channel Beyond The Press experimenting to determine whether a bag of non-Newtonian fluid can stop a cannonball. From what I gathered by skipping around the ten minute video, the answer is a firm no, proving my flexed abs provide significantly better protection against cannonballs than non-Newtonian fluid. "Can you even do a sit-up?" Please, I get out of bed every afternoon, don't I? "You just roll onto the floor." My downstairs neighbors complain about it. So do my knees.
Keep going for the video.
Thanks to lizzy, who agrees this is exactly why castle walls weren't made out of non-Newtonian fluid.