Experiment 248 was the 248th genetic experiment created by Jumba with Hämsterviel's funding. She was designed to terrify enemies into submission with an ear-piercing scream. 248 and the other first 624 experiments were deactivated and smuggled to Earth by Jumba during his mission to capture Experiment 626.
All of the experiment pods were released and scattered across the island of Kauai.
At an unknown point, Experiment 248 was possibly activated in a rainstorm and haunted the Ali'i Trail.
After hiking for half an hour, Stitch detected something with his night vision. He caught a glimpse of 248 inside some bushes and saw a trail of footprints. Stitch then notified Lilo and the others, though Mertle refused to believe it was the Night Marchers.
When it suddenly started to rain, everyone took shelter in a makeshift tent. Lilo, Mertle, Stitch, Jumba, and Pleakley then told each other scary stories. When Lilo finished telling her story, the group heard 248's shrieks, which were mistaken for that of Night Marchers and scared everyone.
Jumba later recognized the scream as one of his experiments, and the group found 248 standing on a rock. Lilo decided to name her Belle, a nickname relating to the term decibel.
Lilo, Stitch, Jumba and Pleakley managed to get a hold of Belle, but she soon ran off into a cave to Gantu, who was pretending to be a Night Marcher to get her. However, Belle's piercing screams were too much for Gantu and Mertle (who had talked Gantu into this earlier), and they begged Lilo and the others to take her.
The first 624 experiments, including Belle, were rounded up by Leroy and taken to a stadium to be destroyed. However, Lilo, Stitch, Jumba, Pleakley, Reuben, and Gantu arrived before the experiments could be destroyed.
Belle did not participate in the following battle between the experiments and the Leroy clones, instead choosing to retreat with the weaker experiments.
The Leroys soon gained the upper hand in the battle but were defeated when Lilo, Stitch, Reuben, and several other experiments performed the song "Aloha ʻOe", which caused the Leroy army to shut down due to the original Leroy's fail-safe.
- Belle is similar to the banshee, a ghoul from Celtic mythology known for its piercing screams, which are usually a sign of doom.
- Belle is named after the mathematical term decibel, a unit used to measure the intensity of sound.
- Belle was activated off-screen.
- Belle is one of two known experiments that lives with Lilo and Stitch, the other being Glitch.
- Belle is one of the few experiments to not appear in the group photo at the end of Leroy & Stitch.