Unguided Lab Tour

A protagonist walks into a top-secret workplace, and no one reacts. We get a quick montage of people doing technical-looking things and glimpses of weird stuff while the spectator walks around in silence, goggling at it all, and still no one reacts.

Only when the audience has had a complete lab tour does anyone notice the visitor, and then the other characters' response indicates whether it is a good lab or an evil one.

This is most common in the Premiere of a Speculative Fiction series. Maybe a Naive Newcomer discovers that his new office is considerably stranger than he expected. Maybe some ordinary guy accidentally stumbles onto a secret lab belong to the villain or Ancient Tradition, and swiftly stops being ordinary. Either way, the audience gets an introduction to the show's favoured brand of Phlebotinum. Extra points if at some point the intruder is shown distorted on the other side of some sciencey looking glassware.

An Unguided Lab Tour can also happen any time a new villain or secret organisation is being introduced to the show. Often an occasion for Exact Eavesdropping. See also Swiss Cheese Security. Sometimes used with the Clipboard of Authority.

Anime and Manga

 * Rins from Black Cat sneaks into Tornero's lab to steal information and discovers human experiments that look like chimeras.
 * Team Rocket in Pokémon the First Movie when they sneak onto the secret island and discover the cloning lab that Mewtwo built there.

Film

 * James Bond does this on occasion, though most of the time he's impersonating someone who has a reason to be there.
 * Pretty much how the portal to John Malkovich's psyche is discovered in Being John Malkovich.

Live Action Television

 * The Torchwood "Everything Changes" used this, after Gwen bluffs her way into the Torchwood base, with the subversion that all the other characters did notice her, they were just pretending to not see her until they couldn't keep it up anymore and burst out laughing.
 * The episode "Random Shoes" does it again with Eugene, although this time they honestly don't notice him because he's a ghost.
 * Came up a couple of times in The X-Files, although these weren't so much secret labs as academic or government labs doing secret things.
 * The Professionals episode 'Involvement' features Doyle's girlfriend wandering into the top secret security organisation CI5 and eavesdropping on an interrogation.

Real Life

 * Probably not all that uncommon in real life, at least for university laboratories.