Light bulb scenes

[Shane]

Light bulb scenes, eureka moments, epiphanies. Call them what you will. These are the scenes on the big or small screen where a character notices something almost by chance, and puts two and two together at supercomputer speed.

There are two scenes in particular that I found particularly memorable. The first is from The Silence of the Lambs, namely the scene where Clarice, oblivious to the fact that she's in the house of the serial killer she's hunting, sees a moth land on a spool of thread and realizes that she's talking to Buffalo Bill. The look on Jodie Foster's face spoke volumes.

The second is from The Untouchables. Elliot Ness (Kevin Costner) has had Frank Nitti hauled out of a courtroom and basically tells him to be a good mobster and wait in the lobby. He then looks for a match for his cigarette and opens Nitti's matchbook, where he sees Malone's address written on the inside cover and realizes that he's found Malone's killer. Bad luck, Frank.

Anyone else got their favourites?

[Scott]

All I can think of is Charlie Chaplin and Virginia Cherrill at the end of City Lights (1931).

But there was also Walter Matthau at the end of The Taking of Pelham One Two Three (1974) which wasn't that great a moment.

There was that thing in The Thin Man when that guy says something that make Nick Charles realize he was the killer. I don't remember it, but the book was better than the movie. 

[Joyce]

How about Heaven Knows, Mr. Allison?  When Mr. Allison and Sister Angela are hiding in the cave while the Americans take over the island they're on from the Japanese.  Mr. Allison suddenly looks up as he realizes how to disable the Japanese big guns to cut down on American losses.  He and Sister Angela feel that God told him what to do.

Robert Mitchum and Deborah Karr.  1957.   Great movie.

[fflurcadwgawn]

Do all of the deductions in the Benedict Cumberbatch BBC Sherlock count? Or I should just limit myself to his best man speech.

As spoiler-free as possible:

Sherlock has to do a best man speech and in the process manages to solve a murder while insulting almost everyone at the wedding. Then there is also the epiphany moment with the new female character where all her little quirks add up to one giant revelation about her past and who she really is.