The idiom 'Blood flows to float pestles' originates from 'Shangshu·Wucheng' (The Book of Documents: The Accomplishments of King Wu), which recounts the fierce battle at Muye near Chaoge during King Wu of Zhou's campaign against the tyrannical King Zhou of Shang. The text exaggeratedly described the carnage, claiming that so much blood was shed that it could float wooden pestles used for pounding grain.

However, the philosopher Mencius later challenged this account, arguing it was an overstatement. He contended that King Wu's army was an army of righteousness, and therefore would not have engaged in indiscriminate slaughter. Furthermore, given King Zhou's cruelty, his own soldiers would likely have defected rather than fought fiercely, making such extreme bloodshed improbable.