The telltale sound made by Lego pieces when the box containing them is shaken or flipped over.
Shaking a box of Lego will give a different sound than turning the box over. The shake produces a much more percussive sound, while the turning over produces more of a waterfall or cascading sound. Both sounds are distinctly Lego.
Often used by children (and adults) to discover the contents of a present.
Physicists have determined that it is impossible to move a Lego box with out getting Lego tinkle.