Simultaneously, you throw your knife at another person who's throwing a knife at you and you both get a dose of your own medicine. Literally, there's poison on these knives and now you've both been stabbed.
"I need a dose of the antidote!" you yell, and the other guy looks you dead in the eyes. They slowly pull a tiny xylophone (ざい) out of their pocket, play a few notes, and then eat it. "Ah, you'd like a dose of the xylophone cure, wouldn't you?"
Currently there are no similar looking kanji which exist in the WaniKani learning system