We conducted an experiment to determine whether people can tell shit from Shinola.
Shinola is a brand of shoe polish once manufactured in the United States. Today we care about Shinola only because it is part of the slang expression “doesn’t know shit from Shinola,” meaning “is completely ignorant.” Shinola is posited for comparison with shit because the two substances have a similar dark brown color and smeary consistency.
The expression now has a special degree of irony. Most people truly do not know shit from Shinola—because they have never heard of Shinola.