'Green stamp' money (file photo)

Top 8: 'Green stamp' money

We usually think that money is interchangeable for all goods and services, but there are exceptions. In some countries, certain currencies can only buy certain things, such as clothes or land. Take Vietnamese bills for example, its edges are basically a bunch of "green stamps" that you should tear off to buy specific things, like a shirt or a pair of pants.

Edible currencies (file photo)

Top 7: Edible currencies

Salt is regarded as one of the oldest forms of payment. In fact, the word "salary" derives from the Latin word "salarium," which denoted the money paid to Roman soldiers to buy salt. In the Middle Ages, salt was the main form of currency across the Sahara Desert, and also proved very popular throughout East Africa. Typically, people would lick a salt block to make sure that it was real and then cut it into small pieces for transaction.

Edible currencies also include "reng," a yarn-ball of turmeric spice wrapped in coconut fibers in the Solomon Islands, cacao in Mexico and Central America, and the parmigiano reggiano -- or parmesan -- cheese in Italy.