If you've ever searched for the same phrase at both Google and Yahoo!, you've probably noticed that the results can be surprisingly different. That's because Google and Yahoo! have different ways of determining which sites are relevant for a particular phrase.
Though we might never know exactly why results are different between the two search engines, at least we can have some fun spotting the differences and end up with more search results than either one of the sites would have offered on their own.
One way to compare results is to simply open each site in separate browser windows and manually scan for differences. But viewing both sets of results in different windows is a bit tedious, and a clever Norwegian developer named Asgeir S. Nilsen has made the task easier, at a site called Twingine. It contains a blank search form into which you can type any search query. When you click Search, the site brings up the results pages for that query from both Yahoo! and Google, side by side. To be fair, the sides on which Google and Yahoo! appear change at random, so people who prefer one side of the screen to the other won't be biased. 
Clicking Next or Previous in the top frame at Twingine takes you to the next or previous page in the search results at both sites.
Surfing the pages in the search results at Twingine can be a bit tricky. You'll probably want to open linked search results in a new window or tab, so that you can keep your place in the search results at both Yahoo! and Google. You can open links in a new window by right-clicking the link (Ctrl-click on a Mac) and choosing Open Link in New Window from the menu. You can also set your search preference at either search engine to automatically open links in a new window when you click a search result.
