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 Big Board operator NYSE Euronext (NYSE: NYX) are living large today, jumping as much as 16.5% on many times the average trading volume.

So what: A fresh buyout proposal from NASDAQ OMX (Nasdaq: NDAQ) and IntercontinentalExchange (NYSE: ICE) has come along to trump the existing offer by German exchange Deutsche Borse. NYSE's board is reviewing the offer and has yet to accept or reject it.

Now what: The NASDAQ/ICE offer of $42.50 per share is actually 19% higher than the old deal, and there's a fair amount of spread between the bid and the current share price. Whoever walks away with the big prize will have created a truly massive, trans-Atlantic stock exchange -- assuming that American and European regulators allow it. That arbitrage opportunity rests on pure uncertainty about the outcome.

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