Google at 20: Googlewhacks, barrel rolls and the search engine's best Easter eggs

Search giant Google is celebrating its own 20th birthday today with a trademark Doodle. Replacing its logo with an occasional animation paying tribute to eminent figures from the worlds of science, the arts and history on their anniversaries is just one of the ways in which the site's programmers can express themselves. Their quirky sense of humour is actually embedded within the software's DNA. If you tell Google to "do a barrel roll", the whole page will spin clockwise at 90 degrees before juddering to a stop. If you search for "the answer to life the universe and everything", you'll be presented with Google's calculator displaying the number 42, an in-joke alluding to Douglas Adams' cult science fiction series The Hitchhiker's Guide to the Galaxy (1978).