When Achilles mother, Thetis, dipped the child into the river Styx, she held him by his heel. It was at that one spot, which did not get wet, that he was vulnerable.The assumption, which seems to be as safe an money in a vault, is that Google will dominate search for years, if not decades, to come. Google holds something between 40% and 50% of the market, more than No.2 and No.3 Yahoo! and MSN combined.The company’s dominance has driven its market cap to $145 billion. Yahoo!’s is $37 billion.But, late word out of the VC community is that someone may be building a better Google.It seems absurd. Powerset, the new search company, has just raised $12.5 million from two fairly well-known Silicon Valley venture funds. To most large internet companies, that’s lunch money.The new Powerset search technology can apparently discern the meanings between related words. It, in essence, understands sentences and phrases.Most investors will look at Powerset and say that such a small company could never be a threat to Google. Which is probably just the way Yahoo! felt in early 2000 when its stock hit $125. (Google started as a research project at Stamfor University in 1996.)Douglas A. McIntyre can be reached at email@example.com. He does not own securities in companies that he writes about.