Page "Crouching Tiger, Hidden Dragon" Paragraph 33

Poison is also a significant theme in the film.

In the world of martial arts, poison is considered the act of one who is too cowardly and dishonorable to fight ; and indeed, the only character that explicitly fits these characteristics is Jade Fox.

The poison is a weapon of her bitterness.

and quest for vengeance: she poisons the master of Wudang, attempts to poison Jen and succeeds in killing Mu Bai.