It will sometimes be handy to write actions that are only available to the non-player characters and not to the player. To do this, we just define an action which has no "understand": the player will never be able to specify this command himself, but other characters can try it.
This is particularly useful for creating abstract or general actions for when we want a character to eat something, wear something, or go somewhere, but aren't too particular as to what the object is; as here, where we just want Clark to move away from the kryptonite, regardless of direction:
Perry White's Office is west of the Newsroom. In Perry White's Office are a desk and a poster of Elvis. On the desk is a lead-lined box. The box is openable. In the box is the green kryptonite crystal.
The Supply Closet is east of the Newsroom. The Elevator Bank is north of the Newsroom.
Clark Kent is a man in the Newsroom. "Clark [if Clark can see the kryptonite]looks a bit ill[otherwise]is here, frowning as he revises his latest article[end if]."