[Splines]

Planet Money had a segment about the rocks-as-currency island:.

Segment: http://www.npr.org/blogs/money/2011/02/15/131934618/the-isla...

Entire podcast (also discusses the currency test, IIRC): http://www.npr.org/blogs/money/2011/02/15/131963928/the-frid...

Very interesting.