Very rapid(ly). The earliest such simile is
quick as a bee, which found a place in John Heywood’s
Proverbs (1546). It was followed by
quick as thought, appearing in Thomas Shelton’s 1620 translation of Cervantes’s
Don Quixote and in Samuel Richardson’s
Clarissa (1748), among other sources. Also common in the eighteenth century was
quick as lightning, with a nineteenth-century American variant,
quick as greased lightning. None but the last is heard much anymore, but
quick as a wink, referring to the blink of an eye and appearing in one of Thomas Haliburton’s Sam Slick stories (1843), is current, as are
quick as a flash, presumably referring to lightning as well, and
quick as a bunny (or
rabbit), which dates from the late nineteenth century. See also
like the wind;
like greased lightning.