In Argentina, warm weather lets sheep graze outdoors year-round. Still, shepherds sometimes came back to find their entire flocks dead overnight. The animals had seemed perfectly healthy during the day; by morning every one had perished. After examining the bodies, bewildered herders found almost nothing—just a few small cuts. Superstitious herders blamed the deaths on “dark forces.”
In reality, the culprit was a small species of vampire bat. Under cover of night, the silent bats swooped down on the flock, nibbled through the wool in spots, pierced the skin, and drained their victims of blood.
To solve the problem, the Argentine government commissioned a short film to show shepherds what was really happening. But how do you film animals that fly only in total darkness when shooting requires bright lights?
The director assigned to the project didn’t give up. He decided to retrain the bats—alter their natural instincts—and after six months he succeeded. The sheep were herded into a separate pen. When the bats attacked, powerful floodlights were switched on. At first the predators fled from the blinding light. Gradually they acclimated. Eventually the floodlights became a signal for them to launch attacks on the sheep.
Unbeknownst to him, the Argentine director had accidentally demonstrated the work of Russian physiologist Ivan Pavlov: conditioned reflexes.
