Roots
Can't remember what we were talking about, but the expression "spill the beans" came up in conversation with Niko the other day. Spill the beans? Well, we had to look it up, even if it was time to get ready for school. One of my first Google options (can't remember what search terms I used) was a promising site that had vanished. I went back and clicked on the cached page, and found paydirt -- a long page that was only the expressions beginning in the letter s.

Spill the beans - reveal information or a secret
An Americanism that may come from bean as US slang for 'head' (spill or let slip what is in one's head). More likely it comes from 'know one's beans' (know what's what); this is clearly related to the early 17th century English saying 'know how many beans make five,' which has the same meaning. It is a short step from knowing one's beans to spilling them, i.e. telling what one knows.

Here's the longer-than-your-arm URL for the cache of the page:
http://66.102.7.104/search?q=cache:zh75RBteqTUJ:users.tinyonline.co.uk/gswithenbank/sayingss.htm+%22spill+the+beans%22+expression&hl=en&ie=UTF-8