The original play was inspired by a trip to Europe made by Murray Burnett and his wife in 1938, during which they visited Vienna shortly after the Anschluss and were affected by the anti-Semitism they saw. In the south of France, they went to a nightclub that had a multinational clientele, among them many exiles and refugees, and the prototype of Sam. In The Guardian, Paul Fairclough writes that Cinema Vox in Tangier "was Africa's biggest when it opened in 1935, with 2,000 seats and a retractable roof. As Tangier was in Spanish territory [sic], the theatre's wartime bar heaved with spies, refugees and underworld hoods, securing its place in cinematic history as the inspiration for Rick's Cafe in Casablanca." The scene of the singing of La Marseillaise in the bar is attributed by the film scholar Julian Jackson as an adaptation of a similar scene from Jean Renoir's film from 5 years before titled La Grande Illusion.The first writers assigned to the script were twins Julius and Philip Epstein who, against the wishes of Warner Brothers, left at Frank Capra's request early in 1942 to work on the Why We Fight series in Washington, D.C. While they were gone, the other credited writer, Howard Koch, was assigned; he produced thirty to forty pages. When the Epstein brothers returned after about a month, they were reassigned to Casablanca and—contrary to what Koch claimed in two published books—his work was not used. The Epstein brothers and Koch never worked in the same room at the same time during the writing of the script. In the final budget for the film, the Epsteins were paid $30,416, and Koch earned $4,200.In the play, the Ilsa character is an American named Lois Meredith; she does not meet Laszlo until after her relationship with Rick in Paris has ended. Rick is a lawyer. The play (set entirely in the cafe) ends with Rick sending Lois and Laszlo to the airport.  To make Rick's motivation more believable, Wallis, Curtiz, and the screenwriters decided to set the film before the attack on Pearl Harbor.The possibility was discussed of Laszlo being killed in Casablanca, allowing Rick and Ilsa to leave together, but as Casey Robinson wrote to Hal Wallis before filming began, the ending of the film "set up for a swell twist when Rick sends her away on the plane with Laszlo. For now, in doing so, he is not just solving a love triangle. He is forcing the girl to live up to the idealism of her nature, forcing her to carry on with the work that in these days is far more important than the love of two little people." It was certainly impossible for Ilsa to leave Laszlo for Rick, as the Motion Picture Production Code forbade showing a woman leaving her husband for another man. The concern was not whether Ilsa would leave with Laszlo, but how this outcome would be engineered. The problem was solved when the Epstein brothers were driving down Sunset Boulevard and stopped for the light at Beverly Glen. At that instant the identical twins turned to each other and simultaneously cried out, "Round up the usual suspects!" By the time they had driven past Fairfax and the Cahuenga Pass and through the Warner Brothers studio's portals at Burbank, in the words of Julius Epstein, "the idea for the farewell scene between a tearful Bergman and a suddenly noble Bogart" had been formed and all the problems of the ending had been solved.The uncredited Casey Robinson assisted with three weeks of rewrites, including contributing the series of meetings between Rick and Ilsa in the cafe. Koch highlighted the political and melodramatic elements, and Curtiz seems to have favored the romantic parts, insisting on retaining the Paris flashbacks.In a telegram to film editor Owen Marks on August 7, 1942, Wallis suggested two possible final lines of dialogue for Rick: "Louis, I might have known you'd mix your patriotism with a little larceny" or "Louis, I think this is the beginning of a beautiful friendship." Two weeks later, Wallis settled on the latter, which Bogart 

Question: When did Mr and Mrs Burnett take a trip?
Answer: 1938