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 hospital company Community Health Systems (NYSE: CYH) were absolutely battered today, losing as much as 45% in intraday trading on heavy volume.

So what: There are numerous ways for a company to fight off a hostile takeover attempt, but alleging fraud by the aggressor is not normally one of them. Tenet Healthcare (NYSE: THC), which has been trying to shake off an attempted $7 billion takeover attempt by Community Health, sued Community, alleging that the company has been systematically overbilling both Medicare and private insurers. Tenet claims that Community's practices may have resulted in billions in ill-gotten profits.

Now what: Community issued a statement that rebuts Tenet's claims and suggests that they are nothing more than an attempt to distract shareholders from the takeover offer. Community also noted that Credit Suisse (NYSE: CS) and Goldman Sachs (NYSE: GS) -- which are providing financing for the transaction -- are still on board. The allegations by Tenet are very serious, though, and there's good reason for Community shareholders to be sweating a bit today.

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Fool contributor Matt Koppenheffer does not have a financial interest in any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.