The tiger keelback (Rhabdophis tigrinus) possesses unusual structures known as nuchal glands in the skin of the dorsal neck. Nuchal glands may contain potent cardiac steroids (bufadienolides) that are secreted when this species is attacked by a predator. The unique anti-predator behaviors of R. tigrinus, such as exposing the neck and neck butting, are presumably associated with the chemical defense of the nuchal glands. Caution