Forestus had an aversion to quacks, charlatans, and the unauthorized practice of medicine. Some of these self-taught healers were considered legitimate, while others were perceived as "quacks". Drakes produce a three note whistle, while hens emit hoarse grunts and quacks. Female Peruvian boobies have a range of vocalizations; from trumpet-like quacks to honks. He also earned money illustrating books of physicians and quacks. The few effective remedies sold by quacks included emetics, laxatives and diuretics. His mother is alarmed and quacks again. He was especially severe on whomever he regarded as quacks. In 1969, the American Medical Association labeled him the "King of Quacks". It should not be confused with the 1939 Bob Clampett short "Wise Quacks". Nasty Quacks is a 1945 Warner Bros. cartoon in the "Merrie Melodies" series. Both "Decline and Fall" and "Quacks" were well received. However, the title, not being protected by law, was adopted by quacks. In 2017 Everett appeared as a recurring character in the BBC 2 comedy "Quacks". "Spy"; and William in the 2017 black comedy series "Quacks".