That giant sucking sound you hear is money -- lots of it -- fleeing stock markets around the globe for the safe havens of the U.S., German, and U.K. sovereign bond markets. It's fear talking -- fear of intensifying crisis in the eurozone.

How bad is it? For the month of May, Japan's Nikkei stock index was down 8.6%. Germany's DAX lost a massive 13.5%. Britain's FTSE plummeted 17.8%. Here in the U.S., the S&P 500 was down a relatively mild 6.7%, but that's not much to cheer about.

This response to the eurozone's latest crisis point is driving bond yields to record or near-record lows:

• 10-year U.K. Gilts are paying just 1.48%, down from 2.1% a month ago.
• The yield on 10-year U.S. Treasuries is just 1.47%, down from 1.95% a month ago.
• 10-year German Bunds are yielding just 1.21%, down from 1.67% a month ago.

The yield on two-year German debt actually went negative briefly earlier this week, meaning investors were so desperate for safety they were willing to forgo any return at all.

Greece + Exit = "Grexit"

After all the eurozone crises we've endured over the past few years, why the rush to the exits now? In short, with what's currently going on in Greece and Spain, it's arguable we might really be approaching the make-or-break point for the eurozone this time.

Last month, Greeks voted overwhelmingly for two parties that campaigned on rejecting the terms of the country's bailout package. Unable to form a coalition, the country will be going back to the polls to try again this month.

It's unclear, however, who will be elected this time and what they will decide to do. If the bailout terms are rejected, it's very likely the other eurozone countries will cut off monetary assistance, Greece will default, and it will be forced out of the eurozone.

Spain + Panic = "Spanic"

In Spain, the government recently had to bail out out one of its biggest banks -- Bankia -- to the tune of $23 billion. That's not a lot of money for the U.S. government, but it's a lot for Spain.

The Bankia bailout is engendering fears that Spain itself will soon need a bailout, and that Europe won't be able to afford it. (Remember, Spain is the eurozone's fourth-largest economy.) And all this is only further driving up the cost of Spanish debt, increasing the possibility the country might need a Greek-style bailout.

No country has ever left the eurozone, so no one knows what sort of economic chaos might ensue -- on either side of the Atlantic -- if one does. In the meantime, investors should prepare for further devaluation of their stock portfolios. It's not over yet.