Upper Couplet: Strong and Weak
Any animal has strong ones and weak ones; the strong ones are because of their constitution, and a good constitution and good nutrition naturally make them stronger than other animals.

Some strong animals always bully the small ones, and the small ones evade and dodge; some strong animals stay on their own territory. They are small animals growing in a nest; some strong ones are three or four times bigger than the weak ones, but the very weak ones may be due to indigestion and lack of sufficient nutrition to supplement. A body without enough nutrition will not grow fast and big.
There are strong and weak, invite you to make a couplet.