One night with the moon, the raven sat in the tree in such a way that it looked like it was holding in its beak the Moon, like a big piece of cheese.
After a while, the fox sees the raven holding a large piece of cheese in its beak and remembering that once fooled him (Fox and Raven by La Fontaine), he starts:
Oh my dear friend, how wonderful you look today! You are the handsomest bird I have ever seen. Oh the shine of your feathers, the regal grace with which you hold your head! Your voice must be as beautiful as you! But I didn't hear you sing!
Immediately the raven began its crowing, but the Moon did not fall, staying further in the beak.
Seeing that she was tricked, the Fox left with her tail between her legs but the raven remained singing until morning.

The raven was so proud of the idea he had that his mood was passed down from generation to generation so even today, when it is night with the moon, all the ravens crowing until morning.