Although we don't believe in timing the market or panicking over daily movements, we do like to keep an eye on market changes -- just in case they're material to our investing thesis.

The stock market opened the holiday-shortened week on a quiet note, with initial optimism about a new agreement with Iran giving way to broader economic concerns. The S&P 500 fell slightly, and even though the Dow held onto a modest gain, Seadrill (NYSE:SDRL), Qihoo 360 (UNKNOWN:QIHU.DL), and Lions Gate Entertainment (NYSE:LGF-A) didn't fare nearly as well. Let's look more closely at what sent these three stocks stumbling today and whether their woes are likely to continue.

Seadrill fell 6% after reporting third-quarter earnings that failed to live up to the high expectations investors set for the ultra-deepwater driller. Revenue growth of 17% was slightly better than expected, but earnings came in light because of a rise in rig operating expenses. Even a 4% boost in its dividend payout wasn't enough to make short-term investors happy, but the overall results validate the company's continued emphasis on ultra-deepwater applications for which demand has been extremely high.

In a similar vein, Qihoo 360 dropped 9% even after reporting a 124% gain in revenue, as adjusted earnings per share rose 135%. Yet a downgrade from Stifel focused less on Qihoo's fundamentals and more on its share-price momentum, given that the stock has more than tripled in the past 12 months. As the company proves to be a solid rival to search-engine leader Baidu, Qihoo 360 seems to be sticking to its growth trajectory fairly well despite increasing competitive pressures from other players in the industry.

Lions Gate Entertainment declined more than 10% despite the fact that the new Catching Fire installment of the Hunger Games franchise had the fourth-largest U.S. opening-weekend box-office receipts ever. Although a few analysts pointed to a higher stretch-goal for the film, most of those following the stock argued that the drop didn't reflect disappointment with the results but rather simply represented a natural pullback after the huge run that Lions Gate's stock has had in anticipation of the release. For long-term investors, the bigger question is how Lions Gate will fare not just with future installments in the series but with other movie franchises once Hunger Games has run its course.