Question

how did the nightingle knew the glow worm​

Answer 1

So, the Nightingale started looking around for something to feast on. Suddenly its eye fell upon a spark on the ground. The nightingale knew at once that he had sighted a glow-worm. It looked down from the top of the hawthorn tree on which it was perched and made up its mind to gobble up the glow-worm in one go.