Sam's piano is the symbolic heart and soul of Rick's Café. All the guests want to sit beside it, in part because they want to be close to Sam, who is one of the most untainted characters in the film. The piano itself suggests purity, which may be why Louis doesn't even think to look there for the missing letters of transit. The music from the piano functions as an opiate, a drug that allows visitors to forget their worries. All is well at Rick's, at least on the surface, when Sam is playing. Sam's resumed playing after Ugarte's arrest, for instance, signals that everything has returned to normal, while his closing down of the piano when Rick and Ilsa first see each other signals that the club's peaceful innocence has been interrupted by painful memories. When the German soldiers take over the piano to play their national anthem, the bar's patrons rise in revolt and defiantly sing "La Marseillaise." More than the arrest of Ugarte, this singing proves the biggest disturbance in the bar, and Louis is forced to shut the place down.
The piano is also a symbol of Rick's heart. Rick forbids the playing of "As Time Goes By" so he doesn't have to wallow in the painful memory of Ilsa and Paris. Like many of his guests, he prefers to forget his pain. When Ilsa requests the song, Sam claims not to remember it, but at her insistence he goes ahead and plays, initiating the re-acquaintance of the former lovers. Sam awakens the song on the piano, and Rick's heart wakes painfully as well. For a while he suffers tremendously, but eventually he seems to come to grips with his aching heart and painful past and to reemerge a better person. Rick will leave Casablanca, but Sam and his piano will stay behind. Having regained his real heart, Rick is free to abandon the piano.
Laszlo is both a character and a symbol in Casablanca. His symbolic elements are rooted in his upstanding, moral personality. Before Laszlo arrives in Casablanca, Rick stirs from apathy at the mention of his name. Laszlo is a symbol of resistance to the Nazis, and his personal conflict of whether or not he can escape Casablanca represents a much larger struggle for power and control. The Nazis officially control the city, but the underground resistance has the support of the majority of the people. The balance of power teeters precariously between the two groups. Laszlo's ability to escape Casablanca will be a sign as to which group may ultimately prevail. That Laszlo was able to escape from a concentration camp and then make his way to Casablanca indicates that the Nazi control over the European mainland is not absolute. If Laszlo can find his way to America, his escape will be a symbol of the power of resistance to Nazi rule. What happens to Laszlo himself is important, but the implications of his fate make up Casablanca's broader themes.
The plane to Lisbon is the best way to leave Casablanca, and it represents the possibility of escape from war-torn Europe and the first, most difficult step of the journey to America and freedom. The letters of transit are the golden tickets out, the exit visas that cannot be refused. Throughout the movie these letters are what everyone wants, and whoever controls or holds the letters has tremendous power. As Casablanca proceeds, the power shifts hands. At first, the civic authority of Casablanca, in the person of Louis, controls the plane's flights, and Rick, who possesses the letters, wields this power and has control of people's fates. Later, Rick transfers the letters to Ilsa and Laszlo, allowing them to depart on the plane. As a result of this exchange, the escaping refugees gain a powerful status as political symbols, while Louis and Rick's own power in Casablanca is weakened. The two self-sacrificing heroes have no choice but to leave the city and start over elsewhere.