The kalack gland is a gland located in Sheyangs, just above their stomachs. This gland collects special enzymes and chemicals from the body, creating a bile that bursts into flame when exposes to oxygen. Sheyangs are able to regurgitate this bile, allowing them to spit balls of fire. Sheyangs are vulnerable when they are attempting to this -- if shot by pulse weapons before spitting out fire, the bile in the kalack gland will ignite into an intense explosion that will kill the Sheyang and any who are near it.
The kalack gland also has the important task of regulating the temperature of the reptilian species. The gland becomes less and less efficient as Sheyangs age -- elderly Sheyang often have trouble producing flame.
Kalack glands are derived from Farscape.