I saw this movie back in the summer of 1968 when I was eleven years old and it scared the pants off me and my friends. We never spoke once for nearly ninety minutes it was so absorbing. And that was unusual for us as we used to lark about a lot in those days - you know?
As I recall, the plot revolves around a group of evil men who have developed a gun which fires little pellets containing a virulent designer fungus, which firstly knocks the victim cold and then consumes his entire body within a matter of hours. One minute you have a living guy - next he's just a mass of green, gungy stuff. Yuk! Horrible.
I think the reason we found it so disturbing was the implied biological warfare element. In other words it could have been possible at that particular point in history, and certainly nowadays in the twenty-first century. So I guess it's still relevant.
I'd love to see this movie again sometime and I give it ten out of ten on the scary scale.