Warren Buffett may be in the process of surreptitiously bagging a pair of elephants. As the investing icon observed in Berkshire Hathaway's (NYSE:BRK-A) (NYSE:BRK-B) latest widely read letter to shareholders, "We continue ... to need elephants in order for us to use Berkshire's flood of incoming cash."

Now, CNBC's Liz Claman reports that "Berkshire Hathaway has bought large stakes -- one of $700 million and another for slightly less -- in two North American railroad companies." This in addition to the Berkshire's stake of close to 40 million shares, or nearly 11%, in Burlington Northern Santa Fe (NYSE:BNI). Buffett did not disclose the name of the companies in which he has the smaller stakes, which are presently but a fraction of the size of Berkshire's position in Burlington.

Publicly held railroads generally have done well of late. CSX (NYSE:CSX), for instance, has seen its share price rise 40% in the past year, while Norfolk Southern (NYSE:NSC) is about flat during the same period, and Union Pacific (NYSE:UNP) is up just under 15% since April 2006. While Burlington's shares have not seen much action over the past year, they did pop 6.5% on Monday, following the release of Berkshire's investment.

Buffett's well known Omaha-based Berkshire Hathaway has stakes in a variety of public and private companies, from manufactured housing company Clayton Homes to MidAmerican Energy Holdings to the Buffalo News newspaper and on to Georgia carpet manufacturer Shaw Industries. His company's largest investments in public companies include stakes in American Express (NYSE:AXP), Coca-Cola (NYSE:KO), and Procter & Gamble (NYSE:PG).

So what other railroads Buffett and Berkshire are currently buying remains anyone's guess. I, like you, would like to know the identities of those two companies. But as Buffett also said in his most recent letter to Berkshire investors -- regarding two public companies whose shares Berkshire Hathaway continues to buy (possibly the rails in question) -- "We don't itemize two securities because we continue to buy them. I could tell you their names. But then I would have to kill you."

All I can say is that I'll be watching the railroad industry considerably more closely than I might have before Buffett's interview with CNBC. But in the interest of my life and limb, I won't pry excessively into specific corporate identities.

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Fool contributor David Lee Smith does not own shares in any of the companies mentioned. He welcomes your comments or questions. The Fool has a disclosure policy.