Whenever there's a special anniversary like Picasso's death, or Einstein, Mozart etc, Google change their standard logo to a logo depicting whatever's being remembered, but the 'doodle' still spells out Google. Yesterday was in celebration of Les Paul so the doodle was an electric guitar and as you dragged your mouse over the strings, it actually played perfect notes - there was a little keyboard icon just below the strings and if you clicked the icon, you could play the notes on your keyboard.
Google: google doodles and you can see all the previous doodles.
Yesterdays doodle was brilliant!