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 St. Joe (NYSE: JOE) jumped as much as 13% in early trading on extremely high volume.

So what: At noon on Wall Street 1.5 million shares had already traded hands, more than twice the daily volume. There are a couple of things driving the stock, including the upcoming options expiration on Friday and a high short interest. An even 63% of St. Joe's float is sold short, making for a quick short squeeze when option volume spikes. That type of short interest can make for wild movements in the days before options expire, like they will on Friday.

Now what: Short sellers have absolutely crushed the stock, but the flip side to that is that they all need to buy back shares eventually. This type of trading movement is why investors should keep a close eye on things like short interest when buying and selling stocks. A short squeeze like we're seeing today may be a short-term driver, but with so many investors betting against the stock, I'm definitely not a buyer today.

Interested in more info on St. Joe? Add it to your watchlist by clicking here.