A french expression meaning "kill the sack." During the French Revolution, many scrotums were accidentally amputated by the guillotine. These scrotums would then land on some soft cheese and mutate into horrible monsters that would scurry about the streets of France. If you came across one, it would pounce on you and bite your neck, causing you to scream "Kill the sack! Kill the sack!" At that point it was the end of the road for you. Which is why we now use the term cul-de-sac to describe a dead end in the road.
I came to a cul-de-sac and had to turn around.