Ninjas used a system called Goshiki-mai, meaning Five Colored Rice, in which rice grains were painted red, blue, yellow, black or purple in order to leave coded messages or trails.
Sharks don't have bones. They are a special type of fish known as "elasmobranchs", which translates into fish made of cartilaginous tissues. Even though sharks don't have bones, they still can fossilize. As most sharks age, they deposit calcium salts
