Washing out the mouth with soap
Washing out the mouth with soap is a traditional form of physical punishment that consists of placing soap, or a similar cleansing agent, inside a person's mouth so that the person will taste it, inducing what is generally considered an unpleasant experience. This form of punishment was especially common in the United States and United Kingdom from the late 19th century until the mid-20th century.
Source: Wikipedia — Washing out the mouth with soap (CC BY-SA 4.0)