Anyway, this doesn't solve the problem with multiple actors.
How do you check the actor in canBeSensed, in case one actor
has discovered the object and another hasn't?
My intuition is that the sense system is the wrong place to be doing
something like that. The sense system answers the question "can x see y,"
not "does x notice y." canBeSensed() doesn't need to know the actor because
it's not answering a subjective question about noticing things; it's
answering an objective question about light rays (or sound waves or
whatever).