The shrieker, a common fungus found in the bowels of the Underdark, is sometimes cultivated by drow societies, creating a first line of defense against intrusion around their cities. In addition, drow alchemists harvest and render the fungus down to a base substance capable of reproducing the shrieker's howl.
Shriek paste is an oily, smelly substance with a slightly purplish color. When smeared on a surface, it retains its same consistency almost indefinitely. When the paste is exposed to a light source equivalent to torchlight or greater, it rapidly crystallizes. During this process, the paste makes a high pitched screeching noise, making it a useful signaling device. The shriek is loud and easy to hear (Listen DC -10, modified as usual for distance, solid barriers, and other environmental factors.) This sound lasts for round before the paste dries up entirely and is rendered inert.