Peradventure this is not Fortune’s work, neither, but Nature’s, who perceiveth our natural wits too dull to reason of such goddess, and hath sent this natural for our whetstone; for always the dullness of the fool is the whetstone of the wits. (43-46)
Cleverly, Rosalind both continues the debate (about which gifts come from Nature and which come from Fortune) and mocks or makes fun of both herself and Celia. The word natural was frequently used to refer to a fool. Thus Rosalind is arguing that Nature sent her servant Touchstone, the Natural, to test their gifts of wit and has revealed that their wits are not truly witty: their wits are like false gold. Rosalind realizes that their little sport is merely foolishness, and both she and Celia would laugh at these remarks.
However, the sport or amusement has been successful. Rosalind has momentarily forgotten her sadness.