Every time you get a flu shot, you should thank a horseshoe crab. Most medical interventions—vaccines, drugs, devices—have been tested on horseshoe crabs. Their blood clots immediately when it's exposed to dangerous bacteria. The biomedical industry bleeds horseshoe crabs routinely in order to make sure their products won't poison patients. But horseshoe crabs are in decline, and an NC company is trying to figure out how to raise them sustainably.