Leucrocotta

Pliny described it as the swiftest of all wild animals. The leucrocotta had the body of a stag, the neck and tail of a lion, cloven hooves, and a mouth that extended the full width of its head — from ear to ear in a permanent, skeletal grin. Instead of individual teeth, it had a single continuous ridge of bone in each jaw, which locked together like a vice.

It lived in India or Ethiopia, depending on the source. Ctesias mentioned it first, and subsequent naturalists elaborated. Aelian added that it could mimic the human voice, calling out names to lure travellers into the wilderness. A man would hear his companion calling from the tree line, go to investigate, and find the leucrocotta waiting with that enormous mouth.

The voice-mimicry connected it to the hyena, which the Greeks already believed could imitate human speech. The leucrocotta may have been an exaggerated hyena account filtered through several layers of travellers' tales, each teller adding details. The continuous bone-ridge for teeth matches the hyena's famously powerful jaw, and the wide gape could describe the hyena's impressive mouth opening.

Solinus added that its eyes were multicoloured and that it could never be captured alive. Hunting parties that pursued it found it simply outran everything — horses, dogs, arrows. Its speed was absolute.

The creature persisted through medieval bestiaries, growing stranger with each retelling, but the core image never changed: that boneless grin stretching ear to ear, calling your name from the darkness.