The Klingon Tea Ceremony is a test of courage. The participants ingested tea brewed from a poisonous plant and recited poetry to each other. Worf stated that this was to teach that "Death is an experience best shared, like the tea."
The tea used was lethal to Humans, and mildly poisonous to Klingons as well. However, Doctor Pulaski successfully completed the ceremony by treating herself with an antidote before the ceremony commenced. (TNG: "Up The Long Ladder")