Every school child knows that Noah's rainstorm lasted 40 days, and 40 nights, but do you know why the magic number was 40, and not, say, 25 or 60?
Rashi provides an answer (Gen 7:4): "Corresponding to the formation of the fetus. Because they behaved depravedly by troubling their Fashioner to fashion the forms of mamzerim.(ie: children born from incestuous or adulterous unions)"
Points to ponder:
(1) A fetus isn't a fetus until 40 days after conception? Alert Operation Rescue!
(2) "Troubling their Fasioner?" In what sense is it a burden for God to cause a fetus to exsit? Isn't this the same Divine Entity who created heaven and earth and all both contain with just a few words?