According to the Google Video Blog, Google has introduced a video search suggestion, in an effort to enhance the user video search experience and also to help viewers discover more interesting videos. Sometimes the suggestions expand the scope of your search, and sometimes they make your search more specific, depending upon what you've been looking for and which suggestion you've clicked on.
To view the search suggestions, click on the "Also try" links on top of the search results to refine or expand your search.
For example, if you are searching for "kittens", you may see suggestions like "cute kittens", "funny kittens", "newborn kittens", "techno kittens", "treadmill kittens" and so on. Clicking on these suggested search terms will lead you to the respective search results page, and another set of suggestions. If you continue following through these suggestion links, your first search may very well turn into hours of exploration.
Google hopes that this new feature will enable users to find what they want and in the process explore other relevant videos as well.