Katharine Hepburn had one very close call with the leopard. She was wearing a skirt that was lined with little metal pieces to make the skirt swing prettily. When Hepburn turned around abruptly, the leopard made a lunge for her back. Only the intervention of the trainer's whip saved Hepburn. The leopard was not allowed to roam around freely after that, and Hepburn was more careful around it from then on.
The scene in which Susan's dress is ripped was inspired by something that happened to Cary Grant. He was at the Roxy Theater one night and his pants zipper was down when it caught on the back of a woman's dress. Grant impulsively followed her. When he told this story to Howard Hawks, Hawks loved it and put it into the film.
This movie fared so badly at the box office that Howard Hawks was fired from his next production at RKO and Katharine Hepburn bought out her contract to avoid being cast in the film Mother Carey's Chickens (1938). Coincidentally, Hepburn was labeled "box office poison" on the same day her contract was dissolved.
Katharine Hepburn had never done any comedy before and had to be trained in gags and timing by Howard Hawks and several veteran vaudevillians he employed solely to train Hepburn. Cary Grant came to the film with his sense of comic timing already impeccably in place.
Cary Grant was not fond of the leopard that was used in the film. Once, to torture him, Katharine Hepburn put a stuffed leopard through a vent in the top of his dressing room. "He was out of there like lightning," wrote Hepburn in her autobiography Me: Stories of My Life.
David's response to Aunt Elizabeth asking him why he is wearing a woman's dressing gown ("Because I just went gay all of a sudden!") is considered by many film historians to be the first use of the word "gay" in its roughly modern sense (as opposed to its archaic meaning of "happy, carefree") in an American studio film. Among homosexuals, the word first came into its current use during the 1920s or possibly even earlier, though it was not widely known by heterosexuals as a slang term for homosexuals until the late 1960s. The line was not in the original shooting script for the film; it was an ad lib from Cary Grant himself.
Katharine Hepburn was generally fearless around the young leopard 'Nissa (II)' who played "Baby" and even enjoyed petting it. Cary Grant was less fond of the big cat and a double was used in the scenes where his character and the leopard had to make contact.
Before the movie was released Cary Grant had been worried that he might never become a major star after all, since he was already nearly 34 at the time of filming and younger actors like Errol Flynn and James Stewart were established stars.
Katharine Hepburn was having a difficult time finding her comedic timing - Hawks said that she was "trying too hard to be funny" and kept laughing out loud. Luckily, Walter Catlett, who played Constable Slocum, was a veteran comic. Hawks wanted him to give Hepburn some tips, but he refused unless Hepburn asked him. So Hawks got Hepburn to ask Catlett for advice. Hepburn was so grateful that she asked Hawks to make Catlett's part larger so that he could be around if she needed more help.
It has been suggested that co-screenwriter Dudley Nichols based the madcap romance on Katharine Hepburn's affair with director John Ford at the time. However, other sources state that Hepburn and Ford were never romantically involved, explaining that although they had been on Ford's yacht together, his wife had been there with them.
Howard Hawks said that he failed at making a good comedy here because of the characters were too "madcap", with no straight men/women to ground it. This comment may have resulted from his disappointment at the film's commercial failure at the time of its release, although many now consider it Hawks' best film.
This film employed a great deal of split screen and optical tricks, such as rear screen projection, so that having the big cat in close proximity to the actors (especially Cary Grant who was more worried about acting with the cat than Katharine Hepburn) could be kept to a minimum. (Hepburn is sometimes shown petting and handling Baby. The leopard's trainer praised Hepburn, stating that Kate was fearless and could become an animal trainer if she so desired.) Most of the split screens had a lot of movement in them, which meant the dividing line had to be moved around as well. Even the scenes of Susan dragging the mean Leopard on a leash are split screened. You can see that the rope does not line up. A puppet Leopard was also used in some shots. It's most clearly seen in the shot after Susan gets the Leopard dragged into the jail. The reaction shot immediately afterwards, shows David and Mrs. Random with "Baby" the Leopard on the table. The Leopard is a puppet.
The theatrical trailer is made up mostly of unused alternate takes of the scenes in the film. For instance, in the take used in the trailer, Cary Grant doesn't jerk downward when Katharine Hepburn rips his coat like he does in the take used in the movie.
The impressive optical effects are discussed in detail in Hollywood the Golden Years: The RKO Story (1987). There is a very informative interview with Linwood G. Dunn who worked (uncredited) on the visual effects for this film. He explains the traveling split screens and points out some visual effects goofs that "got by". Included is surviving footage of the stand-ins for Cary Grant and Katharine Hepburn's in a camera test of the two driving with the leopard in the back.
The final shooting script of the film comes in at 202 pages, which would equal a running time of 3 hours 22 minutes. Whether this amount of footage accounted for the rough assembly cut of the film isn't known.
The script contains an expression that was very common in the USA up until about the 1950s that by today's standards is absolutely unbelievable and (thankfully) would never be used today. In the first scene, when Alice tells Cary Grant's character that "Mr. Peabody may possibly donate a million dollars to the museum", he responds "A million dollars? Say, that's pretty WHITE of Mr. Peabody, isn't it?"