Maybe I didn't explain that part well enough. After cutting the end off of the flare he creates a small hollow area in the part he is keeping, then inserts the wooden plug into the hollow and nails thru the wall of the flare into the wood.

But I doubt that there would be any danger in whacking the filler material in the flare anyway, I don't think that will ignite the stuff. I have hit 'em, run over 'em with a car at high speed, never had a spontanious combustion...