Spare change
(Extracted from http://wiki.mindcloud.org/wiki/Spare_change ;-D)
Why does so much spare change seem to generate spontaneously on desks?
From earlier encounters with loose change, the desk is already permeated with spores. When conditions are right, the spores activate. Eventually, fruiting bodies begin to appear above the surface of the desk - these can be exchanged for goods and services. Make sure that you don't pick them too early or they won't have a chance to renew the spore-bank in the desk!
The cycle can be interrupted by picking the young fruit as soon as they appear - this will have to be repeated many times over as there can be millions of spores on a given desk. Poverty and a cashless economy are also proven to be effective in dealing with a spare change infestation.