In addition to today's animated doodle, Google has released a nerdy little Valentine's Day Easter egg.

If you type the following equation into the search bar, you'll be greeted by a blue heart on a graph: (sqrt(cos(x))*cos(400*x)+sqrt (abs(x))-0.4)*(4-x*x)^0.1.

The hidden gem was first reported last week by Mashable after a mention from Twitter user @Huckleberry, who called it a "nerd heart."

Google periodically releases these Easter eggs, or surprises coded within its search results. In December, it created one with a holiday theme - typing "let it snow" into Google.com produced the normal search results, but shortly after, snowflakes started to fall from the top of the screen, piling up until a virtual snowdrift obscured the screen. Once the digital blizzard obscured the search results page, you could use your mouse to draw in the desktop snow blanket that appeared.

Another popular Easter egg was the "barrel roll" trick, which still works. If you search "do a barrel roll," the results page will first do a 360-degree flip before it settles back into its normal appearance. The page will also do the same kind of spin when you search for "ZZ" or "RR" – a nod to the classic Nintendo game Star Fox 64.

As PCMag reported last year, there's a hidden world of harmless pranks coded just beneath the surface of many popular Web sites like YouTube, Facebook, and Google; undocumented tricks to entertain and amuse. Click on the slideshow below for 12 Easter Eggs and share more in the comments below.