Google Instant is a new search enhancement that shows results as you type. It may not be available to everyone at the moment. http://www.google.com/instant/
I was curious what might happen in the event that you typed a word such as "assume" where the beginning of a word or phrase may bring up unintended search results. Google provides a safe search experience, and seems to assume that you are not done typing the word or phrase. In the event that you decided to search for something like "Equus Africanus Asinus" and used the shortened term "ass" google requires you to hit "enter key" before results are posted. Having google's Safe Search filtering turned on is still good practice.