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 Kronos Worldwide (NYSE: KRO) briefly plummeted more than 16% after reporting strong first-quarter results. The stock has since recovered to down 6%.

So what: This sell-off mystifies me. Kronos, whose titanium dioxide compound is used to brighten everyday products, reported $420.4 million in revenue, up 31.5%, and $1.04 in per share profit, up 19.5%. Wall Street was expecting $400.09 million and $0.79, respectively, according to Yahoo! Finance data.

Now what: What gives? I wish I knew. But maybe it doesn't matter. For long-term investors, today's sell-off could be just the buying opportunity they were seeking. Unlike direct peer Huntsman Corp. (NYSE: HUN), Kronos now trades for a discount to its estimated long-term growth rate -- resulting in a perfectly reasonable 0.72 PEG ratio.

Interested in more info on Kronos Worldwide? Add it to your watchlist.

Interested in more info on Huntsman? Add it to your watchlist.

Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. You can try any of our Foolish newsletter services free for 30 days.

Tim didn't own shares in any of the companies mentioned in this article at the time of publication. Check out his portfolio holdings and Foolish writings, or connect with him on Twitter as @milehighfool. You can also get his insights delivered directly to your RSS reader. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool is also on Twitter as @TheMotleyFool. Its disclosure policy is at least 10% better than other disclosure policies.