“It would be easy to poisen your corn flakes, but astronomically difficult to poisen all the cornflakes in the entire country.”
You would cause much more terror and problems by not infecting the entire batch. Terrorism would involve contaminating only a few selected sites at random locations across the country. It would leave everyone paniced about their cxhances of being the next victim, as opposed to simply not buying corn flakes.
*end rant*