Question

What inspired the nightingale to sing

Answer 1

 if a human sings the nightingale or cuckoo bird hears that if they like our voice they will sing this inspired the nightingale to sing
or
the frog was in a sort of a way an idol of the bird. 
its the authority that the frog enjoyed that inspired the bird to sing

Answer 2

Hey!!!
Ur Answer is "

The over praising of frog inspired the nightingale to sing. This was in the story The Solitary Reaper that tells if a human sings the nightingangle or cuckoo bird will hear our voice, then they will also sing along with us, this inspired nightingale to sing. The over praising of frog also inspired nightingale to sing.

#DudE :-)