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 truck maker Navistar International (NYSE: NAV) jumped 10% today after an activist investor took a stake in the company.

So what: Hedge fund MHR Fund Management has taken a 13.6% stake in the company, larger than Carl Icahn's 11.9% stake. It's unknown what MHR's plans are with the company, but with this fund and Icahn circling, there could be fireworks soon.

Now what: Activist investors often take positions in companies to change management or a company's direction, but all we know right now is that Navistar's current position doesn't look good. The company recently posted a $172 million quarterly loss and guided below expectations. I wouldn't bet against these two activist investors, but with the company posting losses, I'm not excited to buy in right now, either. I'll just stay away and watch the fireworks from afar.

Interested in more info on Navistar International? Add it to your watchlist by clicking here.