Bitter Dumpling (苦団子, Niga-Dango) is a mystic, famous, emetic herbs medicine given to Chihiro by a powerful river god in return for Chihiro's service in Bathhouse.
As its name suggests, it resembles a dango in general shape, and tastes extremely bitter and astringent, as Chihiro found out soon after when curiously taking a bite of it.[1]
Chihiro later fed Haku with a piece of it to cure his internal bleeding, which ended up causing him to egest a curse by Yubaba which took a form of a worm within his body when Haku stole Zeniba's witch seal. Chihiro was saving the medicine for her parents that have been turned into pigs, in the hopes that they will be turned back to normal. In the end, she fed it to a bloated and deluded No-Face which caused him to egest a lot of filth from within his body, and while chasing after her, barfed up the three spirits that he had eaten until when leaving the bathhouse to follow Chihiro to the railway station had reverted back to normal.