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 Herbalife (NYSE:HLF) were gaining ground once again today, climbing as much as 17% after activist Carl Icahn disclosed a 13% stake in the health-supplement maker.

So what: Herbalife has been a battleground stock ever since David Einhorn raised eyebrows with questions about its accounting practices last May. Debate intensified when fund manager Bill Ackman disclosed a massive short position and accused the company of being a "pyramid scheme," and management has since scrambled to defend itself. It found a defender in another fund manager, Dan Loeb, but Icahn's vote of confidence may be more important as he has been right about stocks like these before, most notably Netflix, which has gained about 200% since he bought a 10% stake in the home entertainer in October.

Now what: With Herbalife making a double-digit movement seemingly every week, this stock is clearly for risk-seeking investors only. Personally, I don't believe it's a pyramid scheme as Ackman claims. The multilevel marketing company has been around since 1980, and been publicly traded for eight years. Expect more wild swings from the stock in the future, as this debate is far from over, not to mention that the SEC recently launched an investigation into its business model. Herbalife will report earnings next Tuesday, its first report since the controversy broke, which should lead to some major movement once again.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.