What is the subjective requirement for a tortfeasor to be found liable under the Eighth Amendment under the Cruel and Unusual Punishments Clause?

The subjective requirement relates to the state of mind of prison officials because "only the unnecessary and wanton infliction of pain implicates the Eighth Amendment." Farmer v. Brennan, 511 U.S. at 834. Facts alleged must be enough to show "deliberate indifference" to the health or safety of an inmate. Id. "Deliberate indifference" exists when a prison official "knows of and disregards an excessive risk to inmate health or safety; the official must be both aware of facts from which the inference could be drawn that a substantial risk of serious harm exists, and he must also draw the inference." Id. at 837. "[P]rison officials who act reasonably cannot be found liable under the Cruel and Unusual Punishments Clause." Id. at 845.