In Cervantes v. Walker (9th Cir. 1978) 589 F.2d 424, a county jail inmate was taken to the jail library for questioning about a recent fight. The defendant left his property outside the library as directed and it was searched. A small amount of "a green odorless substance" was found inside a matchbox. (Id. at pp. 426-427.) The searching officer suspected it was marijuana but had no special training in this regard. He took the substance into the library and asked the defendant what it was. the defendant responded: " 'That's grass, man.'" The defendant was placed under arrest for possession of marijuana. (Id. at p. 427.) The court rejected the defendant's argument that Mathis v. United States (1968) requires Miranda warnings in all prison interrogations: "To interpret Mathis as Cervantes urges would, in effect, create a per se rule that any investigatory questioning inside a prison requires Miranda warnings. Such a rule could totally disrupt prison administration. Miranda certainly does not dictate such a consequence. . . . Adoption of Cervantes' contention would not only be inconsistent with Miranda but would torture it to the illogical position of providing greater protection to a prisoner than to his nonimprisoned counterpart. We cannot believe the Supreme Court intended such a result." (Cervantes v. Walker, supra, 589 F.2d at p. 427.) In formulating an appropriate test in a prison setting, the court recognized that the usual test of whether a reasonable person would have believed he was free to leave ceases to be useful. (Cervantes v. Walker, supra, 589 F.2d at p. 428.) Obviously, the inmate is not free to leave. The question must therefore shift to whether some extra degree of restraint was imposed upon the inmate to force him to participate in the interrogation. Four factors are significant in this inquiry: (1) the language used to summon the inmate for questioning; (2) the physical surroundings of the interrogation; (3) the extent to which the inmate is confronted with evidence of his guilt; (4) the additional pressure exerted to detain him. (Ibid.) Subsequent federal circuit court opinions have applied the test articulated in Cervantes to find no Miranda violation. (See U.S. v. Turner (9th Cir. 1994) 28 F.3d 981, 983-984 statements made in telephone call initiated by inmate from jail to postal inspector; Garcia v. Singletary (11th Cir. 1994) 13 F.3d 1487, 1491-1492 inmate removed from his cell and questioned immediately after a fire is discovered inside the cell; United States v. Conley (4th Cir. 1985) 779 F.2d 970, 971-974 one prisoner is stabbed to death and the defendant is discovered with a wrist wound shortly thereafter; he was questioned while in a conference room awaiting transfer to an infirmary and following return from the infirmary; United States v. Scalf (10th Cir. 1984) 725 F.2d 1272, 1273, 1275-1276 following a stabbing in which the defendant was observed in the act, a prison guard came to his cell and asked " 'what was going on . . .' "; the defendant responded that he did not like the victim.) In People v. Anthony (1986) 185 Cal. App. 3d 1114, 1120-1121 230 Cal. Rptr. 268, the Court of Appeal also applied the Cervantes exception where the defendant made incriminating statements to police during telephone conversations from jail that had been initiated by the defendant.