Aruspicy; a fortune telling method practiced throughout history, but most popularly in ancient Greece and Rome. Specifically, the entrails of birds sacrificed on an altar to a particular god were used. The practice was taken very seriously, especially by military generals wanting to know the outcome of an upcoming battle. Today, the method is practiced by voodoo priests and priestesses using chicken entrails.
When used more colloquially, the phrase is derisively used to identify the practice of taking one sample of factual data to (inaccurately) extrapolate a much larger truth -- a polygraph test to identify a criminal, a day's stock market trades to indicate the future of a country's economy, the activity of an area's banks to indicate the likelyhood of a Y2K catastrophe. | 
