It was not until the 15th century that spies were specially trained for their purpose. It was around this time that the word shinobi appeared to define and clearly identify ninja as a secretive group of agents. The ninja were stealth soldiers and mercenaries hired mostly by daimyos. Their primary roles were those of espionage and sabotage, although assassinations were also attributed to ninja. In battle, the ninja could also be used to cause confusion amongst the enemy. Cats just might be ninjas of the animal world, and these images show why. Continue reading for more.