As forest-dwelling animals, they are small and secretive deer, and while their barking call is a handy indicator for humans looking to photograph muntjac, they do most of their interspecies communication through scent. On the faces of muntjac deer are two sets of scent glands; the preoribital which sits just in front of the eyes, and the frontal glands that sit on the forehead. While they’re not the only hoofed mammals to have these glands, they use them for communication more often even than other deer species that live in larger groups.

— Read more in Muntjac Deer Have Bizarre Flaring Scent Glands On Their Face at IFLScience.