The katana had blood on it before the guy killed Dianna’s husband.
Stay tuned for next season......
Stay tuned for next season......"
OMG! I'm going to rewatch right now....
You're right. That blade was covered in blood when Pete swung it back, before he struck Reg with it. We know that Michonne always cleans it off, and that it was indeed clean when she hung it over the mantel.
In the last scene, Michonne's brow began to wrinkle as something seemed to be occurring to her. And why was Carl not right there, wanting to know who broke into the house?
Scary stuff.