Yitsúkar

Jitsukar is a brown paste refined from the venom of the jitsukar, a large clam native to cool freshwater lakes, closely related to the jitsu and jitsutyr, despised as a dangerous pest by fishermen. Jitsukar is prepared by immersing the clams in cold salt water, inducing them to secrete the oily  venom as a protective measure. Some of the oil floats to the  surface, where it is collected and mixed with flowers of  sulfur and  finely ground charcoal to form the sticky paste. Jitsukar kills by destroying the victim's lungs; at minimum, it has no ill effects.