Hi Kevin -   
  
I am not sure if the "fiat money" in the experiment even fits your  
definition--is Joe Monkey using it because Sue Monkey accepts it, and,  
so on, infinitely? Or are the monkeys accepting it because they know the  
human will barter it for food? If so, it is barter pure and simple, not  
a monetary exchange.   
  
It is the typical infinite regress argument. The "nature" of a liability  
is that it must be accepted back by the issuer; this is the fundamental  
characteristic of what you call fiat money. For what? For payment of  
taxes.  
  
Best,  
  
Mathew Forstater