For the "Make 'em Laugh" number, Donald O'Connor revived a trick he had done as a young dancer: running up a wall and completing a somersault. The number was so physically taxing that O'Connor ended up in a hospital bed for a week after its completion. He suffered from exhaustion and carpet burns. After an accident ruined all of the initial footage, O'Connor agreed to do the difficult number all over again.
Donald O'Connor smoked four packs of cigarettes a day during production. "Getting up those walls was murder," O'Connor stated in an interview. "They had to bank one wall so I could make it up and then through another wall. We filmed that whole sequence in one day. We did it on a concrete floor. My body just had to absorb this tremendous shock. Things were building to such a crescendo that I thought I'd have to commit suicide for the ending. I came back on the set three days later. All the grips applauded." However, no one had checked the camera's aperture, and the footage was unusable. "So the next day, I did it again!" O'Connor recalled. "By the end, my feet and ankles were a mass of bruises."
In interviews, Debbie Reynolds stated that she "learned a lot from Gene Kelly. He is a perfectionist and a disciplinarian... Every so often he would yell at me and make me cry. But it took a lot of patience for him to work with someone who had never danced before. It's amazing that I could keep up with him and Donald O'Connor." Kelly commented on her work, "Fortunately, Debbie was strong as an ox... also she was a great copyist, and she could pick up the most complicated routine without too much difficulty... at the university of hard work and pain." After this film, Reynolds and Kelly never worked together again.
A microphone was hidden in Debbie Reynolds' blouse so her lines could be heard more clearly. During one of the dance numbers, her heartbeat can be heard, mirroring what happens to Lina Lamont in the movie itself.
Only 19 years old when cast to play Kathy Selden, Debbie Reynolds lived with her parents and commuted to the set. She had to wake up at 4:00 a.m. and ride three different buses to the studio. To avoid the long commute, she often slept on the set. Finding her asleep, an irate Gene Kelly would shake her awake and urge her to resume practicing her dance numbers. Reynolds began sleeping under the piano on the set in order to hide from Kelly.