The U.S. Supreme Court case Pennsylvania v. Inocencio Muniz, 1989 revolved around the issue of whether or not a suspect's response to a question asked during a sobriety test could be used as evidence against him without violating his Fifth Amendment rights. The defendant, Inocencio Muniz, was arrested for drunk driving and taken into custody where he failed several field sobriety tests. During one such test, an officer asked him when his sixth birthday would be - a question designed to assess mental acuity under influence - which he answered incorrectly. Muniz argued that this constituted self-incrimination and should have been preceded by Miranda warnings (informing suspects of their right to remain silent). The court ruled in favor of Muniz with five justices agreeing that the responses were testimonial in nature and thus protected by the Fifth Amendment privilege against self-incrimination; hence they could not be used as evidence unless preceded by Miranda warnings.

In the dissenting opinion for Pennsylvania v. Muniz, Justice Blackmun argued that the majority's decision to classify Muniz's responses as testimonial was incorrect and inconsistent with previous rulings. He contended that the questions asked by police were routine booking questions, not designed to elicit incriminating responses but rather necessary for administrative purposes. Therefore, they should fall under an exception to Miranda rights established in a prior case (Rhode Island v. Innis). Furthermore, he disagreed with the majority’s view on whether physical evidence could be considered testimonial; he believed it couldn't be because it doesn’t involve communication or disclosure of thought processes which are protected by Fifth Amendment privilege against self-incrimination.