Care of the deceased

What is the significance of a knife placed at an angle on the decease? I've been watching the Taiga drame "Tenchijin" and noticed this.

I seemed to have missed that scene on TV, but even today, typically, the deceased is placed in the coffin with a short traditional knife (along with many other ornaments). The knife is supposed to protect the deceased during the long journey to heaven.

I could be wrong, but I suppose this comes from the samurai tradition, as non-samurai people of the old era usually did not have that kind of a knife at home. So if the knife was featured among many other ornaments in that scene, one can assume that it was a reminder to the viewers that the deceased was a proud family member or the samurai class.