Ami, Yumi, and Kaz speak in Japanese when they are upset, injured, or being shocked. Ami and Kaz's voice actors are Japanese. Yumi's voice actress learned how to speak some of the language in the series thanks to a language coach. This is also evident in the episode of The Grim Adventures of Billy and Mandy titled "My Peeps." Keone Young spoke fluent Japanese and Janice Kawaye spoke some Japanese.
The episode Surf's Up was banned in the United States for its original title, "Tsunami AmiYumi." The episode was set for premiere on December 31, 2004, a few days after the Indian Ocean tsunami. Renegade changed the title of the episode and all the references to the tsunami were changed (the word tsunami was changed into wave). The episode was aired everywhere in the world except in the U.S. where even the edited version was banned. The ban for the edited version can be considered as pointless as the episode was banned only in a country that wasn't affected by the tsunami.
When the show first aired on the Cartoon Network, it scored the highest rating ever for a cartoon premiere.
Up until the premiere of Regular Show (2010), this was the only Cartoon Network show to use licensed music.
The Skull on Yumi's shirt changes to match her expression. (Example: when she's shocked, it makes a surprised face (O_O), when she's happy it makes a smiling face ("_"), and when she frowns, it makes a sad face or scowl.