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 Halliburton (NYSE: HAL) fell more than 15% on massive volume before recovering somewhat after it was revealed that the company may have known the cement it used in the BP (NYSE: BP) well was unstable before it exploded.

So what: A presidential commission found that similar cement had failed Halliburton's own test. The company seems to have mentioned that to BP, but apparently one or both companies failed to do something about it before the well exploded, killing 11 and wrecking the Gulf of Mexico.

Now what: It's not clear yet whether the huge stock slide – which knocked about $2.5 billion off Halliburton's market capitalization -- is warranted. That would largely depend on if the company has been exposed to new liabilities as a result. Oh, Halliburton.

Ilan Moscovitz doesn't own shares of any company mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.