Per 
A victim of SCP-6904's vocalizations.
Item #: SCP-6904
Object Class: Euclid
Special Containment Procedures: SCP-6904 is to be housed in a completely soundproof enclosure. Ear protection offering total sound neutralization must be provided to all personnel requiring access. Monitoring devices should possess no audio recording capability except those used during approved testing. Recordings must be labeled with appropriate hazard communication symbols. SCP-6904 must be fed a live mammal at a rate of approximately 8 kg per day, depending on the amount of preferred tissue available from the prey animal. In the event that prey expires prematurely, fresh prey must be provided or SCP-6904 will discontinue feeding. Deviations in feeding patterns are believed to be deleterious to its long-term health.
Description: SCP-6904 is a large bipedal creature, approximately 2.3 meters and 375 kg. It has some anatomical features of terrestrial birds but all attempts to taxonomically classify it have ended in frustration. Though its appearance has been reported to be disturbing, it poses no serious hazard. SCP-6904’s true danger lies in its vocalizations, which produce a Level-3 cognitohazard. Class-D personnel who have experienced the vocalizations report a bright, high-pitched warbling cry that pulses in a hypnotic fashion. All higher vertebrates with auditory capacity in the human range of hearing are rendered immobile by muscle spasms, in some cases severe enough to fracture bone, similar to a severe infection by Clostridium tetani. Extensor muscles are more affected, leaving the victim outstretched and exposing SCP-6904’s preferred tissues. In 60-70% of cases, victims will present with an arched back, widely opened eyes, and a facial rictus. Victims report extreme pain and a sense of dread at the prospect of being, “… trapped in my own body.”
A victim's facial rictus.
Upon sighting prey and issuing its paralyzing vocalizations, SCP-6904 will then invariably approach and proceed to feed. No attempt is made by SCP-6904 to kill or disable its victims, as the paralysis renders them unable to struggle. Vital organs are usually left undamaged until days later when SCP-6904 has finished consuming its preferred tissues; the superficial flesh of the face, eyes, and neck. In addition to preserving its victims for as long as possible by avoiding their vital organs, SCP-6904’s saliva contains a coagulant that functions to prevent appreciable blood loss.
SCP-6904 poses little threat to personnel wearing required ear protection as it moves more slowly than average human walking speed and does not seem interested in ambulatory prey.
Powerful muscle relaxers have been successful in terminating the muscle spasms induced by SCP-6904’s vocalizations, but in ██% of cases, victims require █-██ weeks of rehabilitation to regain the use of [REDACTED].
Addendum 6904-01:
In vivo study of brain tissue affected by SCP-6904's vocalizations using Thaumaturgy Enhanced Magnetic Resonance Imaging (teMRI) has revealed that exposure causes immediate depolarization of the primary auditory cortex located in the superior temporal gyrus. The exact mechanism of how this cortical disruption propagates from the auditory centers to the motor cortex while leaving the cortical substrate of consciousness unaffected remains unknown. Signal analysis of the vocalizations has revealed nothing illuminating with respect to etiology but has established that electronic recordings of sufficient fidelity remain hazardous to humans.
Addendum 6904-02:
Observations of SCP-6904’s grooming and nesting behavior indicate that it likely belongs to a social species and that the particular specimen in containment may be experiencing pathological tendencies brought on by long-term captivity. Going forward, SCP-6904’s environment should be populated by no less than three stimulating objects. Stuffed animals have shown positive results but should be replaced periodically.
