Nicholas Theocarakis wrote:  
>Samuel Bostaph said:  
>> If you recall, Bob Hebert presented a very amusing paper at the SEA several  
>> years ago (and I think it was subsequently published) asking why dogs would  
>> trade one bone for another anyway.  
>  
>Recall also Edwin Cannan comment on WoN I.II: "It is by no means clear what   
>object there could be in exchanging one bone for for another."  
>  
>Nicholas Theocarakis  
  
People go to "swap meets" all the time.  
Not to mention "garage sales."  
  
As a Boy Scout, I would spend hours at conventions ("jamborees")  
swapping my "patches" for others.    
("Patches" are sewn insignia.)  
I had several that were exactly alike, so naturally I was interested in  
swapping most of them for others all different.  
  
But in an even simpler situation, one tires of a music recording,  
or an article of clothing, and it is easy to imagine  
wanting to make a like-kind exchange for something equivalent  
but different.  Or swapping a book that you've read  
for one that you haven't read.  
  
I can't speak to bones.  
  
Martin C. Tangora