high-school presentation, suggestions?

I'm going to present something about the exact sciences to high-school
students I never met.  In the area of mathematics or computer science,
what would be a nice short presentation?  What is the computer about?

My best idea for the moment is to present what the computer does par
excellence.  What does the computer do par excellence?  I think it's
simulations.  I have a personal story involving a simulation that sort
of shows what the computer is about.

When I was very young (about 8 years old or something like that), there
was a very charming person in the building I lived who invited me to
play a card game called WAR.  We went to the playground and I was taught
the game, which was very simple even for an 8-year-old.  It turns out
the game was very boring even to an 8-year-old.  You split the deck of
cards and each player takes half of the deck.  Cards faced down.  Now
each player puts a card face up on the table.  The player with the
highest card wins the table.  If it ties, then the table accumulates and
each player opens up a new card until one wins.  The objective of the
game is to win all your opponent's cards.  We played with two decks of
cards, which made the game last a long time.  I did not ever want to
play it again.  So it stayed with me that this is the most boring card
game I ever.

Anyway, many years later now I was one weekend at my sister's and
talking to my nephews I came up with the idea---hey, wanna play the most
boring card ever?  You know children.  They said a loud---YES!  So we
did it.  Remarkably, they seemed to enjoy themselves and competed
against each other.  (They never played it again, though!)

Anyway, that was on a Sunday.  I came back home at the end of the day
and kept thinking about that game for the first time.  I asked
myself---could this game ever repeat on forever?  You see, I was worried
with my nephews that I'd be stuck at that table forever.  Luckily, the
game ended again about half-hour later.  (We played with a single deck
of cards.)

So I decided to make a simulation.  I wrote the code and ran the game.
What I found surprised me.  On the computer, after the two players's
cards were face up on the table, the player who won the table would take
the cards all in the order they were placed.  The fact that this order
was not changed seemed to have made the game very likely to repeat on
forever.  Using a sample of 1000 game runs, the probability that a game
would end was 0.128, about 13%.  So the probability of a never-ending
game seems to be about 87%.

I then decided to run the game such that the player who won would
shuffle the cards before putting them back at the end of his stack of
cards.  Doing the simulation this way results in the game ending nearly
always---99% probability.  Now, I'm saying 99% because I simply did not
find a single game run that went on forever.  (But I don't think the
probability is 100%.  But the statatistic /is/ 100%.)

I asked myself---why does the shuffling make the game likely to end?  I
don't know.

Bottom-line is that the computer is a lot of fun.  It can see things
that we would likely never see it ourselves without it.

And that's my idea for the presentation.  It's about the computer.  It's
about what I think the computer does best---simulate other things.  And
it's about very interesting things such as probability.

It's personal.  It's real.  And it's funny: I was an 8-year-old very
excited to play a new game, but then I realized the game just kept me
staring along the luck of each half of the deck for about an hour. :)
(But it was worth it!  The game was boring, but my opponent was very
interesting.)

Any cool ideas you might want to suggest me?  Thanks!