Surah 12. Yusuf, Ayah 17

They were surprised that Jacob received the story about the wolf with cold incredulity. So they grew petulant, put on an air of injured innocence, and bring out the blood-stained garment described in the next verse.

They wanted to make out that they were not negligent of Joseph. They were naturally having games and exercise, while the boy was left with their belongings. It was the racing that prevented them from seeing the wolf. And Jacob's fears about the wolf (xii. 13 above) made them imagine that he would swallow the wolf story readily.