the common law rule preventing the admission of hearsay, that is to say, testimony by one witness as to the statements and observations of another person to prove that the statement or observation was true. The rationale was that the defendant had no opportunity to challenge the credibility of and cross-examine the person making the statements. Certain exceptions to the hearsay rule have been permitted; for instance, admissions by the defendant are admissible, as are dying declarations. Nevertheless, in California v. Green, , the Supreme Court has held that the hearsay rule is not the same as the Confrontation Clause. Hearsay is admissible under certain circumstances. For example, in Bruton v. United States, , the Supreme Court ruled that while a defendant's out of court statements were admissible in proving the defendant's guilt, they were inadmissible hearsay against another defendant. Hearsay may, in some circumstances, be admitted though it is not covered by one of the long-recognized exceptions. For example, prior testimony may sometimes be admitted if the witness is unavailable. However, in Crawford v. Washington, , the Supreme Court increased the scope of the Confrontation Clause by ruling that "testimonial" out-of-court statements are inadmissible if the accused did not have the opportunity to cross-examine that accuser and that accuser is unavailable at trial. In Davis v. Washington , the Court ruled that "testimonial" refers to any statement that an objectively reasonable person in the declarant's situation would believe likely to be used in court. In Melendez-Diaz v. Massachusetts, , and Bullcoming v. New Mexico, , the Court ruled that admitting a lab chemist's analysis into evidence, without having him testify, violated the Confrontation Clause. In Michigan v. Bryant, , the Court ruled that the "primary purpose" of a shooting victim's statement as to who shot him, and the police's reason for questioning him, each had to be objectively determined. If the "primary purpose" was for dealing with an "ongoing emergency", then any such statement was not testimonial and so the Confrontation Clause would not require the person making that statement to testify in order for that statement to be admitted into evidence. The right to confront and cross-examine witnesses also applies to physical evidence; the prosecution must present physical evidence to the jury, providing the defense ample opportunity to cross-examine its validity and meaning. Prosecution generally may not refer to evidence without first presenting it. In Hemphill v. New