To throw up, Australian slang dates from the 1920s. There are two theories about its origin. The first is that it is an abbreviation of the naval expression watch under, meaning look out below, shouted as a warning before a sailor threw up aboard ship. The second, and perhaps more likely one, is that it is rhyming slang, Chunder Loo/spew. Chunder Loo was a popular cartoon character in a series of long-running advertisements for Cobra Polish in the early 20th century.