In the 1938 film "Bringing Up Baby" the baby wasn't a baby at all. What was it?

"Bringing Up Baby" is a 1938 American screwball comedy film directed by Howard Hawks, starring Katharine Hepburn and Cary Grant, and released by RKO Radio Pictures. The film tells the story of a paleontologist in a number of predicaments involving a scatterbrained heiress and a leopard named Baby. The screenplay was adapted by Dudley Nichols and Hagar Wilde from a short story by Wilde which originally appeared in Collier's Weekly magazine on April 10, 1937.

The script was written specifically for Hepburn, and was tailored to her personality. Filming began in September 1937 and wrapped in January 1938; it was over schedule and over budget. Production was frequently delayed due to uncontrollable laughing fits between Hepburn and Grant. Hepburn struggled with her comedic performance and was coached by another cast member, vaudeville veteran Walter Catlett. A tame leopard was used during the shooting; its trainer was off-screen with a whip for all its scenes.

"Bringing up Baby" was a commercial flop upon its release, although it eventually made a small profit after its re-release in the early 1940s. Shortly after the film's premiere, Hepburn was infamously labeled box-office poison by the Independent Theatre Owners of America and would not regain her success until The Philadelphia Story two years later. The film's reputation began to grow during the 1950s, when it was shown on television.