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 reinsurer Flagstone Reinsurance Holdings (NYSE: FSR) collapsed again today, falling as much as 10.4% on heavy trading.

So what: Some of Flagstone's rivals also swooned on Friday when the massive earthquake hit Japan, pretty much in lockstep with their respective exposure to Japanese disasters. But Flagstone wasn't done falling, and it's taking another hit today, bringing the combined two-day fall to 20.8%.

Now what: Insurance can be a risky business, and reinsurance doubly so, because a company like Flagstone has nowhere else to pass the buck when bad comes to worse. Even if you think the market is overreacting here, recovery is by no means guaranteed. United Fire & Casualty (Nasdaq: UFCS) arguably still hasn't recovered from Hurricane Katrina, for example, despite being a well-managed business with committed leadership. When Mother Nature strikes, it seems as if nobody is safe.

Interested in more info on Flagstone Reinsurance? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. United Fire & Casualty is a Motley Fool Hidden Gems recommendation. Try any of our Foolish newsletter services free for 30 days. 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 is investors writing for investors.