Where Does the Phrase “Spill the Beans” Come From?

"Spill the beans" is a common idiom, but why are beans being spilled?

The phrase “spill the beans” means to reveal information that was meant to be kept private. An example of it in a sentence is: “He spilled the beans about the surprise party.” There are a few possible explanations for where “spill the beans” came from. One explanation dates back to ancient Greece when people would use beans to vote anonymously. White beans were used for positive votes, and for negative votes, black beans or other dark-colored beans were used. These votes were cast in secret, so if someone knocked over the beans in the jar—whether by accident or intentionally—they “spilled the beans” and revealed the results of the votes prematurely. Phrases that mean something similar to “spill the beans” include:

Letting the cat out of the bag
Leaking a piece of information
Squealing