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.

After last week's report from China that the country's manufacturing industry was slowing, investors sent the major indexes lower for the fifth consecutive day today. The Dow Jones Industrial Average (DJINDICES:^DJI) lost 41 points, or 0.26%, while the S&P 500 fell 0.49%. But of the three major indexes, the Nasdaq lost the most, down 1.08%. Since the technology-heavy index was by far the worst performer, let's look at which companies helped pull it lower.

Shares of Google (NASDAQ:GOOGL) dropped 2.01% during the regular trading session and then another 0.38% in after-hours trading. The move comes on the heels of Google's announcement that it's paying $400 million to buy Deep Mind, a European company developing artificial intelligence. This is Google's largest European purchase, and it comes as Google has been eating up robotic companies. Investors may be showing concern that Google is steering away from its core business of advertising, which could lead to lower profits and a weaker company. I don't think these moves will hurt Google in the long term, but they do make me wonder where the company is heading.  

Meanwhile, Facebook (NASDAQ:FB) tumbled 1.65% during the trading day and another 0.84% after hours. Facebook will turn 10 years old on Feb. 4, and some investors are concerned that the company is no longer the "hot" thing in social media, as reports indicate that younger users are turning to other platforms. On the other hand, Twitter dropped 6.2% during the regular trading session and LinkedIn fell 5.6% today, so the overall sector decline may mean social-media stocks have a larger problem on its hands than just defecting teenagers. As for Facebook, its earnings release is scheduled for Jan. 29.

Finally, although Apple (NASDAQ:AAPL) closed the day up 0.81% and technically helped the Nasdaq today, shares ended the extended trading session down 7.98%, or $43.00. The company reported better-than-expected revenue and earnings per share after the bell but gave lower-than-expected guidance for the coming quarter. Management believes it will post second-quarter revenue within a range of $42 billion to $44 billion, while analysts were estimating $46 billion. That has investors concerned that growth at the innovative technology company may be slowing. So even though Apple may have not hurt the Nasdaq on Monday, it certainly looks as if it will on Tuesday.