When I first read the review I thought, "That can't be right — most of what is being described can be done with existing biotech — you don't even need nanotech". So I called Scott and the devil is in the details. What he is really objecting to in the movie is that single nanobots cannot contain or manufacture enough material to kill someone "instantly". I would tend to agree with him on that. I suspect some minutes might be required. More typically an hour to a day or more. Of course one could get around this by simply injecting a lethal dose of such nanobots. I suspect that dose can be made quite small.