I have a cat named Bebber. He is very sociable, and cuddly, and cute, and also occasionally disturbingly intelligent. Like, “Thank goodness we had you neutered, or you and your hyper-intelligent army of many-thumbed kittens would have taken over the world by now” intelligent.

Yesterday he decided to…
1. Bring home a mouse.
2. Spit out mouse on kitchen floor. *ptooi*
3. Make sure Attendant Human was watching.
4. Walk to kibble jar, start thwatting with paw. Looked at mouse. Looked at Attendant Human. Looked back at jar; continue thwatting. Repeat.

My cat has just invented the economy. Granted, he is operating under the (unfortunately flawed) assumption that his humans want mouses, and would agree to exchange said mouses for goods and services, so his particular currency system needs a little tweaking before it will work. But… well.