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Although Watson routed the humans in the first "Jeopardy" match, its Final Jeopardy question left everyone scratching their heads.

The Final Jeopardy category was "U.S. Cities." Watson said, "What is Toronto?" with multiple question marks denoting its lack of confidence. The clue was: "Its largest airport is named for a World War II hero, its second largest for a World War II battle." The human players, Ken Jennings and Brad Rutter, both got the right question ("What is Chicago?"), but Watson still finished with $35,734. Jennings had $4,800 and Rutter had $10,800.  

Despite an otherwise impressive performance, Watson was soundly mocked on Twitter for the final mistake. "The machines don’t know all. Yet," posted @erickohn.

The Double Jeopardy and Final Jeopardy rounds of the first game aired Feb. 15. The first round of "Jeopardy" had been broadcast on Monday, and the second game of the two-game tournament is scheduled for Wednesday.

Watson’s odd answer was a result of several confusing factors, according to David Ferrucci, whose post-game analysis appeared on IBM’s A Smarter Planet blog. "Jeopardy" category names are tricky because they "only weakly suggest" the expected answer, so Watson tends to downgrade the significance of the category name when calculating its answer, Ferrucci said. If the question had included "U.S. city" in the question, it would have given U.S. cities more weight in its search, he said.

Watson was also probably confused by the fact that there are several cities named Toronto in the United States, and the Canadian Toronto has a baseball team in the American League, according to Ferrucci. "Chicago" was the second answer on Watson’s possible list, according to A Smarter Planet.

For more, read the eWeek article: IBM’s Watson Wins in ‘Jeopardy,’ Needs Lessons in U.S. Geography.