여우구슬
Korean for "fox bead", a [b]yeou guseul[/b] (sometimes romanized as "yeowoo guseul") is a small, marble-like ball associated with "kumiho":https://en.wikipedia.org/wiki/Kumiho, the Korean version of the [[kyuubi|nine-tailed fox]] spirit.

Often a kumiho keeps her yeou guseul in her mouth, and can use it to steal the life force of humans with a kiss.
yeou guseul