Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of railroad operator Kansas City Southern (NYSE: KSU) fell 10% on Tuesday after its quarterly revenue came in below Wall Street expectations.

So what: While the company's fourth-quarter profit rose a whopping 85%, a big miss on the top line -- $530.3 million versus the consensus of $550.3 million -- is triggering fears of a looming slowdown. Of course, KCS shares have been on fire over the past few months -- up about 45% since late September -- so Mr. Market might have just set the expectations bar a little on the high side.

Now what: I'd look into this pullback as a possible buying opportunity. "KCS continues to have abundant growth prospects and is very well-positioned to be a leading growth company in the transportation industry," said CEO David Starling. "We believe that in 2012, KCS will continue on a growth trend similar to that of the past year with mid-single digit increases in volumes and pricing." When you consider that KCS' Mexican assets make it a particularly tasty takeover target to boot, the stock seems like a pretty decent bet.

Interested in more info on KCS? Add it to your watchlist.