Speaking of that, a thorny issue in IF library design is how generally to define verbs. If actors aren't portable, for example, you might decide to have the verb take only apply to objects (which is the Alan default anyway), or even a Portable class defined for this purpose. But often it makes sense to try picking something up even if the game
won't actually allow it. For example, your cat. And even for obviously fixed objects, you may want to customize the failure message, or even toggle the portable flag, e.g. if the hero suddenly develops superpowers! So be as general as possible.