In "Spike", Experiment 319 (Spike) runs amok in the Museum of Natural History until he is eventually captured by Stitch, but not before spiking him and Jumba with his goofiness-inducing spines, although Spike's spines didn't affect Jumba (since he was already a genius) as much as Stitch.
In "Yaarp", Gantu captures Stitch, who was posing as Experiment 613 (Yaarp), mistaking him for the experiment. Gantu then negotiates with Lilo and tells her to bring Yaarp to the Museum of Natural History for a ransom exchange. When Lilo arrives with Yaarp in a pet carrier, Gantu is wearing special earmuffs in case Yaarp should try to emit any destructive shock waves. Lilo manages to convince Gantu that she has rehabilitated Yaarp, and that he won't cause any problems. However, when Gantu removes his earmuffs and barters Stitch for Yaarp, the latter unleashes a sonic blast upon Lilo's signal, which alerts the authorities. When the authorities try to arrest Gantu, he flees the museum, realizing he was in trouble and outmatched. Yaarp is shortly after revealed to the mayor and chairwoman, who seem surprised at how such a small creature can make such a big noise.