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.

The Dow Jones Industrial Average (DJINDICES:^DJI) woke up on the right side of the bed this morning, gaining 45 points at the open. Following a 12% bounce since October, it wouldn't be a surprise to see stocks pause as we head into the final trading days of 2013. Still, news is breaking this morning on a few companies whose shares could see heavy trading in today's session, including Twitter (NYSE:TWTR), General Motors (NYSE:GM), Textron (NYSE:TXT).

Twitter is down 3.3% after it was the focus of an article in The Wall Street Journal today that noted the stock's nearly 80% rise this month has come despite bearish Wall Street analyst ratings and no significant news from the company. And yet trading volume in the stock has spiked higher in recent days, even as the broader market saw lower volume due to the holidays. Sure, the microblogging site has made some enhancements to its apps that should boost the service's appeal to both users and advertisers. But it's hard to justify a valuation of almost $41 billion -- on par with search giant Yahoo!'s market capitalization -- for the as-yet unprofitable company.

GM is recalling 1.5 million vehicles through its joint venture in China over concerns about a fuel pump bracket that could crack after heavy use. The issue affects two popular brands in the country, the Buick Excelle and the Chevrolet Sail, which explains why the recall is so large. Still, the move appears to be strictly precautionary, so it shouldn't be a threat to GM's business there. The automaker recently reported that sales are up an impressive 11.4% in China so far this year . GM's stock is down slightly in early trading .

Finally, Textron is up moderately after announcing that it is expanding its fleet by purchasing privately held Beechcraft. The deal is expected to cost $1.4 billion and will boost Textron's portfolio by adding popular aircraft brands like the King Air turboprop and the AT-6 light attack military plane to its offerings. Textron also plans to benefit from Beechcraft's global network of 90 service centers. The transaction will be funded with cash and as much as $1.1 billion in new debt.