The concept of money is kind of crazy when you think about it.

We're one of the only known species that have orchestrated complex social structures that are based solely on the acquisition of imaginary numbers of "wealth" - and that's been a human concept for a very long time. It started with territories, then resources, then those resources were represented with currency, and that currency changed into many shapes and forms over the years from stones, to metals, to a specific metal that's not really useful for anything except being particularly shiny, then paper, and now, digital numbers.

It's bananas that our entire worth as a member of our species is universally measured by a completely fabricated system of monetary rules (that are often broken) in order to gauge individual success. It really is insane.

So it must seem kind of strange to animals who scrounge and hunt for their food, to see human beings exchange pieces of paper for the things that they want.

But that doesn't mean they're not willing to participate in that system, if it means they're going to get fed. Just ask Negro, the black dog who lives on the Diversified Technical Education Institute of Monterrey Casanare in Colombia.

Negro is the school's unofficial mascot. He has a sweet demeanor and is loved by the students, faculty, and staff at the school. They give him food, shelter, and water and in return he looks after the place.

During his "security rounds" on the campus grounds, Negro noticed that the school children were buying snacks from a stand in between their classes. Seeing that the students were exchanging what looked like leaves, for cookies, he decided to go and engage in some commerce himself.

Teacher Angela Garcia Bernal spoke with The Dodo about Negro's unique approach to securing some treats.

"He would go to the store and watch the children give money and receive something in exchange. Then one day, spontaneous, he appeared with a leaf in his mouth, wagging his tail and letting it be known that he wanted a cookie."

Gladys Barreto, who's worked at the school cookie stand for years, says that Negro's been paying for treats with leaves for quite some time.

"He comes for cookies every day. He always pays with a leaf. It is his daily purchase."

Now even though Negro is adorable, workers at the school are sure to not let the pup overindulge. They only feed him treats that are dog-digestive friendly, and they limit the amount of "purchases" he can make in a day so he doesn't get too rotund.

Although Bernal, and everyone on campus, is used to Negro's behavior by now, they still recognize just how special of a dog he is.

"When you first see it, you almost want to cry. He's found a way to make himself understood. He's very intelligent."

He's become somewhat of a celebrity on the school's official Facebook page, as well.

Negro isn't the first dog who learned the concept of money to pay for things.

The Pankun and James series in Japan was full of instances where a curious Chimp (Pankun) and his plucky bulldog sidekick (James), participated in all sorts of "human" challenges. Like the time they boarded a train all by themselves, after getting a practice run by his teacher and mentor a day before.

Then there was this black lab who was trained to use actual money to pay for treats by her owners.

There are some instances of animals embracing the less-savory aspects of commerce.

Like this group of monkeys who had money introduced to them. Soon after understanding the "value" of their money, the monkeys began exchanging it for sex.

Then there was this adorable Shiba-Inu who ran the cutest cigarette stand in all of Japan.