The Adventure of the Cardboard Box

A Prank or a Crime of Passion? Sherlock Holmes is up to something. He doesn't believe Inspector Lestrade's story that Miss Susan Cushing is a victim of a prank. She received a parcel with two human ears packed in a coarse salt. And what about the precarious cuts? Or the writing and the spelling correction from the parcel? Doesn't these clues suggest something more than a prank made by a bunch of medical students?