Google replaced the celebrated logo on its home page on Tuesday with a mysterious collection of colorful dancing balls.
Pointing a mouse at the blue, green, red and yellow balls makes them change shape and fly around the screen. The balls then regroup to form the Google logo, or "doodle" as it is known at the California company.
Google did not provide any explanation for the new doodle and the Internet was rife with speculation about what it might mean.
Some Web commentators noted that Tuesday is Google's 12th birthday while others said the doodle may have to do with a press conference about search the Internet giant is holding on Wednesday.
Google added to the mystery with a cryptic message on its Twitter feed.
"Boisterous doodle today. Maybe it's excited about the week ahead...," it said.
The Mountain View, California, company frequently changes the colorful logo on its famously sparse home page to mark anniversaries or significant events or pay tribute to artists, scientists, statesmen and others.
Google, for example, recently marked the 30th birthday of Pac-Man by featuring the classic arcade videogame in a playable doodle.
Explore further: Supreme Court allows challenge to Colorado Internet tax law