Why Does This Deer Have Moving Holes on Its Face? the Viral Muntjac Mystery Explained

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The muntjac head features four prominent facial scent glands: two preorbital (or suborbital) glands located directly anterior to the medial canthus of the eyes, and two frontal glands running vertically down the center of the forehead inside the V-shaped ridges leading to its small antlers. Unlike static skin pores, these are deep invaginations of the epidermis lined with sebaceous and modified apocrine secretory tissue, supported by robust involuntary cutaneous muscles.

During passive activity, the glands remain closed, appearing as modest dark creases across the deer’s facial profile. However, when the muntjac becomes aroused, excited, curious, or confronted with potent olfactory cues, the surrounding facial musculature pulls the pocket inside out. This eversion reveals pale, glandular inner walls dripping with oily, pungent musk secretions. The animal can open either set independently or flare all four in unison, creating the disconcerting optical illusion of extra blinking eyes or supplemental nostrils flexing in synchrony.

Musk production serves as an invisible identity card. Each deer’s secretion contains a unique cocktail of volatile chemical compounds, including ketones, fatty acids, and aromatic esters that convey the individual's sex, reproductive readiness, emotional state, and rank within the local hierarchy. When Biscuit caught the scent of human-provided food, the autonomic surge triggered facial contractions that pulled the gland pockets completely open to sample ambient odors while discharging territorial musk.