h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Does this scale judge how real something is or simply how counter-intuitive something might seem? Certainly, we expect that the future will resemble the past; but is this assumption justified?

My question is this,

"If a gerbil knocked on my door and asked me for some bedding, should I be surprised or should I invite him in and offer him tea?"

Now, Hume pointed out quite well that we cannot derive an "ought" from an "is". Therefore, though my understanding of the workings of the world is limited to gerbils that don't actually speak, should one speak to me politely, I cannot say that I shouldn't be polite in return. I'd like to think that should a gerbil decide to knock on my door and ask me for bedding(or sugar, for that matter) that I'd even invite him to stay for dinner and perhaps later, after retiring to the den for coffee, I'd delicately approach the question of how in fact he -- as a gerbil -- is able to speak. But I cannot say with any certainty that I would. If I were to react otherwise(screaming and hitting it with an umbrella and such), would that be wrong?