A fishing harbour had a shark problem where all of a sudden sharks of all sizes swam near the harbour. It was too difficult to try attack the big (大) ones so a fisherman decided to catch small (小) sharks before they grow big.
magnitude, size, measurement, large and small, at any rate, adults and children, and consideration of seniority
The little shark took a bite of the dangling (dà) bait and the fisherman rejoiced and shouted (xiǎo) to his helper for support.
da4 xiao3 and da xiao