Pre-condition: object must be audible; that is, it must be within hearing range of the actor. This condition doesn't attempt any implied command to make the object audible, but merely enforces audibility before allowing the command.

It is possible for an object to be in scope without being audible, since an object can be inside a container that is transparent to light but blocks all sound.

We enforce this condition with a verification test.

objAudible :   PreCondition