Rutherford Manor Haunt
I wonder if you could layer Worbla over a knife template of craft foam? I think that might work?
Yeah, I saw the same video. I was in a hurry to make some fake needles this last season and didn't have time to spray paint them silver, so I went the suggested metallic tape route. I don't think you could have noticed the difference unless you're looking at them pretty closely and in good lighting (neither of which is the case in a haunt.) I'd definitely suggest this route for the knife.Another thought... Adam Savage (of Mythbusters) used metallic foil tape (used on ducting) over a wooden sword to make it look like shiny steel.
You could find a cheap plastic or rubber job with the right shape, and make the blade look dangerous.