Nosy behaves exactly the way he was designed and programmed. He will somehow try and discover any juicy info that can be listened to, read, or unveiled in any way, and uncaringly nose his way through other people's business. He will also tell anybody whatever he has managed to dig up, mostly embarrassing things. This is useful when needing to know plans from friends or enemies, but otherwise useless since Nosy likes to gossip about humiliating secrets rather than items of strategy, due to his glitch.
One of Nosy's most biggest characteristics is his rather big mouth. Not just literally – he could talk for long hours about stuff. He is also shown to be very emotional and sensitive, as he was seen crying after Pleakley managed to tame Spike during the E.A.R.W.A.X. seminar. He can hold a grudge, especially when it comes to things that are pinned on himself, such as never being rescued from his capture. Last of all, Nosy is never a fighter – when a battle comes his way, he will run away screaming rather than stand up and fight for himself.
Experiment 199 was the 199th genetic experiment created by Jumba with Hämsterviel's funding. He was designed to snoop out and unveil his enemies' most humiliating secrets, but due to a glitch in his program, he preferred juicy gossip to anything important. 199 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 after this, Experiment 199 was activated.
199, disguised as a kid, had watched the new Wasp Mummies movie, then exited the theater and revealed the secret ending aloud to Lilo and Stitch before sauntering off. Stitch, at that moment, saw through 199's disguise and captured him. 199 then rummaged through Lilo's duffel bag and dug up her diary.
Lilo and Stitch later took 199, named Nosy, back to their house, where he began to snoop out and unearth numerous secrets.
When Keoni and his father arrived at the Pelekai residence, invited to brunch, Nosy intervened by unveiling the Pelekais' secrets to the Jamesons. He first blurted out that Stitch, Jumba, Pleakley and Nosy himself were actually aliens, and then mentioned Lilo's obsessive crush on Keoni.
As a result, Stitch got rid of Nosy, slammed a container over him, and handed him to Gantu as a present. Delighted, Gantu expected Nosy to disclose all of Lilo and Stitch's experiment files. Instead, he talked about useless information and revealed secrets about Gantu to Experiment 625, prompting Gantu to send Nosy to Hämsterviel.
At the prison asteroid, when Nosy revealed Gantu and Reuben's secret disrespect towards Hämsterviel, the latter sent him back to Gantu as revenge (though Nosy first was able to steal Hämsterviel's diary). Nosy read Gantu Hämsterviel's diary, but the former was then kicked out of Gantu's ship for the trouble he caused.
Thus, Nosy returned to the Pelekais' home, where he gossiped constantly and even exposed Stitch as an alien genetic experiment after their tussle. However, he was shortly after recaptured by Gantu, which Lilo and Stitch allowed him to do without hesitation. Back at Gantu's ship, Nosy and Reuben exchanged rumors about Gantu.
In "Spike", Nosy was one of the experiments in Pleakley's E.A.R.W.A.X. group. He revealed to everyone that Pleakley's antenna was prematurely orange and simply dyed green before being reprimanded. Shortly after, Pleakley used Nosy in his aromatherapy (in which he rubbed Nosy with a smelly fish). When the other experiments later began to cause chaos, Nosy was chased by Spike through the house. Near the end of the episode, Nosy tried out Pleakley's hugging-and-crying therapy.
In "Woops", Nosy was sent back to Gantu after Experiment 600 caused mischief and nearly blew Hämsterviel's cover to the prison guards. Afterwards, Woops accidentally smashed open Nosy's containment orb, allowing him to escape.
In "Snafu", Nosy traveled to the Pelekais' house, angry with Lilo for abandoning him and the other captive experiments to Gantu. He also revealed when Gantu's ship was empty and spied on Gantu and Reuben, who were foiled by Experiment 120 while attempting to revert all of the rehabilitated experiments to evil using a recording of Angel's song.
The first 624 experiments, including Nosy, 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.
Nosy 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.
- Nosy bears a great resemblance to Pain from Hercules in both appearance and personality, and even sharing the same voice actor, Bobcat Goldthwait.
- Like Reuben, Nosy is one of the very few known experiments that can speak English rather fluently.
- His name is derived from both his abnormally-sized nose and the adjective meaning "to show too much curiosity about other people's business."
- In "Spike", Nosy was seen at Pleakley's E.A.R.W.A.X. group, but Gantu captured him. Though he could have temporarily escaped somehow.
- Nosy's pod color is purple.
- Nosy is described by the experiment computer screen as, "Experiment 199. Primary function: Digs up dirt."