Spooky...kepala otak kau

I got this link in an email from my boss with the subject line: "Fw: This is spooky!!!" There was a string of about a dozen forwarded email headers with comments like "Crazy! I tried it twice and both times it was right on. Weird……": Wizardry

Cookies for the first person who can figure out how it works. (Post your answer in comments.) Extra chocolate chips for anyone who can figure out why (mathematically) it works. Took me about five minutes to articulate my answer. Hint: it has a lot in common with similar "think of a random colour" or "write down your name and add up the ordinal values of all the letters" mind-reading tricks, but this has a bit of a twist.

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How it works:

Every ninth symbol is the same - that is, the symbols do change each time the game is run, but in each run, all multiples of nine have the same symbol. This means that the function given in the instructions must always give a multiple of nine, giving gullible players (i.e. 99.9% of Internet users) the impression that a Flash game is somehow reading their minds.

I thought to look for this pattern because multiple of nine have funny properties due to us having ten fingers - for example, some of the "pick a random number" children's tricks mentioned above depend on the fact that if you add the digits of a multiple of 9, the result will equal 9. (An extension of the trick depends on the tendency of people to think of "elephant" when asked for a gray animal, and "Denmark" when asked for a country that begins with D, but that's the vagaries of the English language, not the vertebrate skeleton.)

Why it works:

The most straightforward way I can think of to explain is like this: If you take a multiple of 10 (e.g. 40) and subtract the first digit, then the number you get is a multiple of 9:
10x - x = 9x (e.g. 40 - (4+0) = 36, 70 - (7+0) = 63).

So any other two digit number is just incrementing that by whatever additional amount:
(10x + y) - (x + y) = 9x (e.g. for 43, (40+3) - (4+3) = 36).

What really baffled me was one of the forwarded comments, "I've tried it about 20 times and it was right every single time."
Like, hello, woman, if you've tried it twenty times you should have noticed SOME kind of pattern. Alamak, oi.