What does Genesis 37:31 mean?

With Joseph out of the way, sold as a slave and bound for Egypt (Genesis 37:12–30), the brothers turn their attention to concocting a story to tell their father. An extravagant example of Jacob's favoritism was the ornate robe he had given Joseph (Genesis 37:3–4). The brothers kill a goat and smear the blood on Joseph's multi-colored garment. This would give the appearance that Joseph had been mauled by a wild animal. Most likely, they took other steps to mangle the garment, making it look like something they'd recovered after an attack.

Yet again, deception continues to play a key role in the history of this family. At the urging of his mother, Jacob deceived his father by covering his hands with the skin of slaughtered animal (Genesis 27:15–17). Now his children deceive him with the blood of an animal, as well.