A more thorough explanation:

A hot-water ordeal is a type of trial in which an accused person is subjected to a dangerous or painful physical test, with the result being considered a divine revelation of the person's guilt or innocence. This type of ordeal was commonly used in Europe until the 13th century, but only sporadically after 1215, when the Fourth Lateran Council forbade the clergy from participating in ordeals.

One example of a hot-water ordeal is the ordeal by water, in which guilt or innocence was determined by how quickly the accused person's arm healed after being placed in boiling water. Often, the person was forced to retrieve a stone from the bottom of a pot of boiling water. The person's hand and arm were then bandaged and, upon the bandage's removal three days later, were examined for festers (indicating guilt). Another example is the hot-water ordeal, in which the accused person was submerged in hot water and the judgment of guilt or innocence depended on how quickly and cleanly the person's body healed.

These examples illustrate how the hot-water ordeal was a primitive and often cruel method of determining guilt or innocence, based on the belief that God would reveal the truth through physical tests. However, the results of these ordeals were often unreliable and led to innocent people being punished or even killed.