A character wants to eavesdrop what's happening on the other side of a door or wall. Putting their ear against the door isn't quite enough (maybe all they can hear is who's talking, not what's being said), so they put a drinking glass against the door and put their ear against that. How does this work? When sound waves enter the glass they resonate against the sides. Thus they can stack up until the sound is loud enough for you to hear. This strategy is indeed Truth in Television. You can try this at home! Note that glass creates an amplifying resonance a lot easier than other possible materials.
ExamplesAnime and Manga
- Akane does this in the Ranma ½ manga.
- Carl Denham does this in Peter Jackson's remake of King Kong in order to listen in on what the producers are planning for his movie.
- In Good Omens, Brian makes an innocent remark about his grandmother using a glass to listen in on her next-door neighbours. Though he doesn't seem to consider the implications, we're left to infer that she hears some raunchy stuff and yet keeps on eavesdropping.
- Deconstructed on The Office (US). Kelly puts a glass to a wall in order to hear the conversation on the other side. When a character asks if she can hear them, she says "Yes, they're saying murmurmurmurmurmur".
- I Love Lucy had Lucy using this several times during the duration of the series to eavesdrop on Ricky.
- Jesse Pinkman does this in Breaking Bad, listening in on Jane's flat.
- In one episode of Hi-de-Hi!, Yvonne and Barry Stuart-Hargreaves use a glass to eavesdrop on Gladys Pugh and Jeffrey Fairbrother in the neighouring chalet.
- WKRP in Cincinnati. Les gets a mail-order "Sneaky Snooper" which is a jelly jar (or as Les claims, it's disguised as a jelly jar) with an antenna attached to it. He hopes to break some big stories with it.
- Doctor Who. The Doctor does this in The Eleventh Hour to hear the voices on the other side of the crack in young Amy's bedroom wall.
- Friends. The tenth season opener (set in Barbados) has Ross in bed with Charlie in one room, Joey in bed with Rachel in another, and everyone else listening at walls in the room between. No glasses used, but their absence is regretted.
- Subverted in an episode of The Dick Van Dyke Show where Rob uses the glass the wrong way 'round and gets milk in his ear.
- Glee. Some New Directions members do this in the first sectionals episode in order to eavesdrop on the judges' deliberations.
- This is one of the puzzle solutions in SPY Fox : Operation Ozone. You need the combination to Poodles Galore's safe to use her rocket, so Professor Quack provides Spy Fox with a gadget resembling an ordinary glass. He puts it against a window where employees at Ms. Galore's factory are on break and talk about the irregular safe combination because it's a Mad Libs Combination of words related to cosmetics rather than a number.
- One of the Mini Games in Mystery Case Files: 13th Skull involves eavesdropping on one character this way.
- Near the beginning of Ed, Edd 'n' Eddy's Big Picture Show, as the Eds are hiding from the rampaging cul-de-sac kids in Eddy's brother's room, Edd hears through the door to see if they are at the present location using a glass cup found in the room.
- On an episode of Muppet Babies, highlighting comic strips, Piggy imagined herself to be Mary Worth listening in on her neighbors with a glass.
- Wayside plays with this. They use the claim you can hear through the wall with a water glass, so Myron uses it to listen against Sherry's head while she's asleep.
- American Dragon: Jake Long. Jake Long'' is sent to the principal's office. His friends Trixie and Spud stand outside with glasses of water trying to listen, but Spud doesn't get that he has to put the glass to the window and his ear to the glass for it to work, as Trixie tries to explain.
Hello, Unknown Troper. You'll need to get known to lend a hand here.