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The penny finally dropped

Posted by RRC on April 23, 2008 at 16:15:

In Reply to: The penny finally dropped posted by Bruffy on April 23, 2008 at 15:00:

: Has anyone else heard the explanation that the projectionists, in the early cinemas, put a coin in the end of the first reel of two-reel movies and placed the reel-can under the projector. As the projectionists had seen the movies before they slept and waited for the penny to drop into the can and wake them up. Frankly this is a more meaningful explanation regarding "waking up to a realization" than pennies dropping into lavatories.

If this was indeed a widespread practice, no one heard the coin drop but the projectionist. How did the phrase come to be popular? Did projectionists go around boring everyone with long stories of how they do their jobs?

The OED's first cite is 1951 - does this fit into the idea of "early cinemas"?

The cinema penny's drop is expected and anticipated. Does that fit in with a sudden, unexpected realization.

Lavatories were given as an example of a coin-operated machine. I imagine every child has probably experience the frustration of a hesitant jammed gumball machine.