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 3-D movie technology specialist RealD (NYSE: RLD) sank as much as 12% in intraday trading Tuesday, with more than 500,000 shares already changing hands versus the average three-month volume of 415,000.

So what: It's hard to know what's driving today's heavy sell-off, but when you couple RealD's 50%-plus run-up over the past three months with some recent box-office weakness, strong bouts of profit-taking should be expected. Over just the past three trading sessions, RealD shares have shed about 18% of their value.

Now what: Even with today's double-digit decline, RealD remains far too risky to take a chance on. While RealD has more than 9,000 theaters in operation, rival IMAX (Nasdaq: IMAX), with just 350 theaters, remains the technologically superior and established way to play the whopping growth of 3-D. When you consider that RealD also trades at a forward P/E that is higher than IMAX's, the decision is that much easier.

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

Fool contributor Brian Pacampara doesn't own a position in any of the companies mentioned. IMAX is a Motley Fool Rule Breakers choice. Try any of our Foolish newsletter services free for 30 days.

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