Scooby has a speech impediment and tends to pronounce most words as if they begin with an "R"; however, most characters are able to understand him almost perfectly. In most iterations, he keeps his sentences relatively short, usually using charades for anything longer than three or four words. His catchphrase, usually howled at the end of every production, is "Scooby-Dooby-Doo!" or "Rooby-Rooby-Roo". Scooby was voiced by Don Messick through "Arabian Nights" in 1994, after which point Messick quit smoking; quitting smoking changed his voice and prevented him from achieving the same raspy vocal effect (despite Messick's efforts, he suffered a career-ending stroke in 1996 and died in 1997, before any further "Scooby-Doo" productions were made). Messick is also known for providing the voice of the dogs Astro on "The Jetsons" and Muttley (who snickered). The characteristic speech impediments of Scooby and Astro are so similar that Astro's signature phrase, "Ruh-roh!", is popularly and improperly attributed to Scooby (as in "Ruh-roh, Raggy!"); of the two voices, Scooby's had a deeper and throatier timbre than Astro's.