|"I know how to make a poison that is colorless and odorless, completely untraceable. It causes a person to pass quietly, as if he'd simply fallen asleep."|
|— Ursa explaining the poison to Ozai.|
When Ursa learned that Azulon had ordered Ozai to take Zuko's life, she struck a bargain with him: she would give him a poison that was completely untraceable to do as he wished with it, and in return, he would spare Zuko's life. Ozai agreed to the deal, but only if Ursa promised to leave the Fire Nation Capital and never return, fearing that she would use it on him as well. After making the poison, she handed it to Ozai and left without saying a word to him. The next day, Azulon was dead, and Ozai became the new Fire Lord.
The poison is a colorless and odorless solution made by heating a combination of herbs. Individuals who ingest the poison die what appears as a natural death, given that it does not elicit any symptoms.