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 health-care service provider Tenet Healthcare (NYSE: THC) are doing a fine impression of a dying swan today, falling as much as 20.2% on more than 10 times the average trading volume.

So what: Tenet jumped drastically in January when rival Community Health Systems (NYSE: CYH) offered to buy the company. Today's freefall comes as Tenet rejects the offer in rather violent fashion, filing lawsuits against Community and generally kicking like a cornered mule.

Now what: Community's shareholders are suffering even more than Tenet's today, as the proposed merger of equals would have created enormous synergies and built an instant mastodon. Market leader SunLink Health Systems (AMEX: SSY) is the logical winner if this deal falls through, and that stock is naturally soaring today. I think a merger would benefit both Community and Tenet, but some highly qualified members of Tenet's board disagree. If this is a stalling tactic, designed to conjure up a better offer, it's a highly elaborate and risky one.

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