Bulbapedia states that the words to make Walda laugh consist of random characters that are determined by the player's Trainer ID number. Players can try entering random characters until Walda laughs, or they can use a code-generating website.
The website Filb.de will generate a secret word that will make the sick girl laugh. To enter the code, players need to go to Rustboro City and enter the house north of the Pokemon Center. The old man there will ask for the funny word. If players enter a word that makes Walda laugh, they will receive a special wallpaper. To generate the funny word, players need to enter their Trainer ID, language and information about the wallpaper they want. This includes the hex codes for the background and foreground colors, the background pattern and the icons to appear on it.