It was approximately the size of a small cat, with a brownish-yellow hide and bright red eyes. It had dorsal fins used both for cooling and for gliding, with which it could dive and attack its prey by biting. Though small and relatively harmless, its teeth injected a complex and lethal venom into a victim's bloodstream. Over a timescale of minutes to a few hours, the venom inflicted waves of intense, clawing pain, briefly immobilizing the victim while affecting their strength. Following a successful attack, a slethi retreated and hid, but then followed its dying prey until it eventually collapsed.