Here is a distressingly easy hypothetical. Police say they want to question you about your involvement in a crime. You say, "I plead the Fifth." Query: Have you invoked your rights under the Fifth Amendment to the United States Constitution.
Shockingly easy, right?
Yet three conservative judges on the Ninth Circuit Court of Appeals would have held that saying, "I plead the Fifth" does not communicate to the police that you want to invoke your rights under the Fifth Amendment. Simply amazing.