The goblin and the grocer

A goblin lived with a grocer whom he liked a lot because, at Christmas, the grocer never forgot to give him his porridge with a big knob of butter. Under the eaves of the grocer's house lived a student that the goblin had disliked at first sight. But, one day, when the goblin wanted to play a prank on the student, he discovered something that would transform his peaceful existence.