1. lit. to sleep on brushwood and taste gall (like King Gou Jian of Yue 勾踐|勾践[Gou1 Jian4]), in order to recall one's humiliations) (idiom)
2. fig. to maintain one's resolve for revenge
3. lit. to lie on firewood and taste gall (idiom); fig. suffering patiently, but firmly resolved on revenge