This section of Misce-Looney-Ous serves as a definitive guide to the Looney Tunes and Merrie Melodies shorts that reused animation from earlier films.
As a way of saving time and money, cartoon studios reused animation drawings from earlier shorts in new cartoons. At Warner Bros., this practice was most frequently employed during the 1930s (the Great Depression era). It began to decline somewhat during the 1940s and, with Bob Clampett's departue in 1946, its use fell drastically. By the 1960s, reusing animation was overshadowed by other cost-cutting methods. Yet, it was still used a few times during this decade.
A distinction should be made between reused animation and reused gags. Reusing animation, as discussed above, means reusing older animation drawings for a new cartoon. By contrast, to reuse a gag means that only a certain scene from an earlier cartoon is reused without using any animation drawings from previous shorts (the material is completely new).