A friend of mine who teaches European history at Washington University in St. Louis once told me about a time he spotted a plagiarized term paper. He summoned the student to his office.
"This isn't your work," he said. "Someone typed it for you straight out of the encyclopedia."
"You can't prove that!" the student sputtered.
My friend smiled and showed him the paper. Circled in red was: "Also see article on communism."