As you move your mouse closer to the logo, the balls repel away in an explosion of multi-colored dots.
Google has been known to turn its homepage over to so-called "doodles" before but, usually, the colorful animations coincide with an important holiday or Google milestone.
Google's latest doodle did not come with any explanation and when asked about it by ABCNews.com, a company spokesman offered the statement, "Today's doodle is fast, fun and interactive, just the way we think search should be."
When the U.K.'s Telegraph asked earlier if the animation was to mark a milestone or promote a new product, a spokeswoman said, "We will leave the mystery to you."
Across the Web, the theories are percolating.
Some think the illustration is to mark what could be the company's 12th anniversary, though the exact date of Google's birth is somewhat up in the air.
On Sept. 4, 1998, the company filed papers establishing it as a California corporation. But the company has sometimes celebrated the occasion on Sept. 7 or Sept. 27.
A few years ago it gave up on the specifics and posted a page saying, "Google opened its doors in September 1998. The exact date when we celebrate our birthday has moved around over the years, depending on when people feel like having cake."
But according to the blog Search Engine Land, the bouncing balls have nothing to do with Google's birthday.
"Today's doodle is not related to a birthday," a spokesperson told the blog. The spokesperson also repeated the statement that the doodle is "fast, fun and interactive."
Search Engine Land suspects that the bouncing balls imply that the company will announce something "fast, fun and interactive" at a search event it is hosting tomorrow.
Google, the world's largest Internet search engine, posted its very first doodle in 1998 and its first animated doodle earlier this year to celebrate the birthday of Sir Isaac Newton (it showed an apple falling from a tree). To celebrate the 30th anniversary of the popular arcade game Pac-Man earlier this year, Google unveiled a logo that doubled as a game Web users could play straight from Google's homepage.