Looking for a movie or Show
 

For atleast 10 years I been looking for a strange movie, It has to do with a knife. Now I'm not for sure if someone is holding the knife or if it has a mind of it's own cause all you would see is the knife. I THINK I remember a scene where it was hiding behind something and it killed I think an old lady in a wheel chair and she fell down the stairs and her head came off. It was a black and white film I believe. Please help me, it would mean alot if you could.

so.....someone gets killed by a knife

hmmmmm....this should be an easy one.