In 1902, mattresses were often sacks stuffed with straw or hay (hence the similar phrase 'hit the sack').
Given the many B-feature cowboy movies in which the bad guys, or occasionally the pesky redskins, would 'bite the dust', we might expect this to be of American origin.
To divulge a secret, especially to do so inadvertently or maliciously.
Fall to the ground, wounded or dead.
Go to bed.
The derivation of this expression is sometimes said to be a voting system used in ancient Greece. The story goes that white beans indicated positive votes and black beans negative.
It isn't though. The same notion is expressed in the earlier phrase 'lick the dust', from the Bible, where there are several uses of it, including Psalms 72 (King James Version), 1611:
The term hay was used in the USA to mean bed since the early 20th century
Votes had to be unanimous, so if the collector 'spilled the beans' before the vote was complete and a black bean was seen, the vote was halted.
