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 Prestige Brands Holdings (NYSE:PBH) are trading nearly 12% lower today after the company took an ugly swing and completely whiffed on both its earnings and its forward guidance for the full year.

So what: Wall Street had been expecting revenue of $156.8 million and earnings of $0.39 per share for Prestige Brands' fiscal third quarter. But the company came in with revenue of just $146.2 million (a 9% year over year decline) and $0.30 in EPS. Worse still, Prestige Brands now expects to finish the full year with EPS in the range of $1.48 to $1.52, which is weaker than its earlier EPS guidance of $1.65 and well below Wall Street's $1.67 consensus.

Now what: Prestige Brands blamed the weak quarter on "inventory reductions as a result of soft foot traffic, the return of several competing brands to the marketplace, and a weak cough/cold season." When you can't sustain your momentum once competitors get back in the game, that raises concerns about your value proposition as a company and as an investment. On the other hand, this latest guidance update pegs Prestige Brands' full-year growth at roughly 20% over its last fiscal year. That's still respectable for a company that boasts a P/E of just 15.6. You might want to keep a closer eye on this stock, particularly if it slides further into value territory.

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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.