Most of the 3D buildings that appear in Google Earth have been sketched by independent designers, some of whom managed to sneak in easter eggs of their own.  Spin round to the waterfront side of the Sydney Opera House in Australia and you'll find a model of the late wildlife expert and adventurer Steve Irwin wrestling a crocodile.  The suggested links that appear in the bar above GMail inboxes are - depending on your view - entertaining, irrelevant or annoying. But you can't help but smile at the recipe ideas that appear in the same bar of the spam folder.  The menu includes Spam Confetti Pasta, French Fry Spam Casserole and Spam Breakfast Burritos, and best of all they link to real recipes.  The search engine's "did you mean" feature helps even the worst spellers locate useful results. But type "recursion" into the search box and it suggests "recursion" as an alternative, sending you on a loop of clicks that all generate identical results. Word play, Google-style.  5) Talk to a martian  The Mars feature of Google Earth 5 allows users to explore the surface of the Red Planet - and chat to the locals. Typing "Meliza" into the search box takes you to an area of the planet where you can strike up a conversation with a martian.  But don't expect anything too deep. The martian's chat is powered by Eliza, a rudimentary artificial intelligence application that aims to replicate human interaction, but doesn't really succeed.  6) The meaning of life  Douglas Adams' The Hitchhiker's Guide to the Galaxy is the geek bible, and it seems that Google's engineers are big fans. Type "answer to life, the universe and everything" into the query box and "42" comes out as the top result.  Other phrases that generate tongue-in-cheek answers from Google Calculator include "number of horns on a unicorn" and "once in a blue moon".  7) Google Earth flight simulator  As if soaring above the planet wasn't enough, Google Earth allows users to fly an F-16 fighter jet anywhere in the world.  Simply press Ctrl + Alt + A to activate the rudimentary flight simulator; you can learn the controls here. The simulator was originally inserted as an easter egg but has since become one of the official features of the programme.  The name may not be familiar but you'll undoubtedly have seen examples of ascii art on the web. It has become a catch-all term for any images made from keyboard characters, and has maintained its popularity despite the obsolescence of the early text-only computers where the style originated.  Googlers are so fond of ascii art that they alter their doodle whenever anyone searches for the phrase.  This easter egg is almost impossible to stumble upon, but fortunately Google employees have spilled the beans. Search for "Niniane kicks ass" in Google Maps are you are directed to the tech firm's headquarters in Mountain View, California, where an engineering manager called Niniane Wang worked until this year.  As Mrs Wang explains on her personal website, her name was inserted into the Google Maps coding after she won a dinner-time bet with a colleague.  Want to find something online but too lazy to type? Just stare into the spinning circle on Google Mentalplex, and project an image of what you want to find. Google claims that the results are "smarter and faster" than normal searches, and generated by an algorithm that factors in your recent browsing history and mouse movements, plus the current air pressure and astrological configuration.  While not an easter egg per se - it was an April Fool's Day prank in 2000 that has been kept online - MentalPlex is a great examples of Google's prankish sense of humour.  Early versions of Google Maps took an optimistic approach to long-distance travel. If you requested a route between locations separated by expanses of water - say Paris and New York - the software dutifully provided road directions to the west coast of France before suggesting that you "Swim the Atlantic Ocean (3,500 miles)".  Whether a genuine easter egg or just a programming error, the swim option has now been withdrawn.  12) Mountain View on Street View  If you spent years designing something, it's only fair that you get to be in it. Dozens of Google employees lined up to be captured by the Google Street View camera car as it passed their California headquarters.  One even dressed up as "pegman", the draggable Street View icon.  Google has created several spoof versions of its homepage, including one for Klingon speakers, another for pirates, and a third specifically for Looney Tunes character Elmer Fudd.  They function just like the normal Google search engine - only the buttons are different.  14) Blues Brothers bridge jump  Another 3D buildings easter egg hidden inside Google Earth, this time recreating the famous bridge jump scene from Blues Brothers, the 1980 movie starring John Belushi and Dan Aykroyd.  That was filmed in Chicago, but the stunt is reproduced for Google Earth on the Tacony Palmyra bridge linking New Jersey and Philadelphia.  15) Don't clog the tubes!  Typing "about:internets" into the search box of a Google Chrome browser brings up the image above.  It is believed to be a reference to Senator Ted Stevens' much-derided 2006 description of the internet as a "series of tubes". His clumsy words, in a speech to a Senate committee opposing network neutrality, were seen to illustrate the poor understanding of some politicians about how the internet worked.
Google loves to slip in-jokes and hidden features known as "easter eggs"   into its products. Here are 15 of our favourites.