There are no simplistic Answers to a complex problem. It is similar to the problem with prophecy; I myself have once fallen victim to the dratted thing.

[The old man talks absently as he yet again fetches a bottle from a shelf. After a brief search of his desk, he recovers a fresh eye dropper and squeezes the eyes out of it, leaving it ready to be filled with a small amount of the new potion. After doing so, he hands the now eyeless dropper to the duck, who takes it cautiously in her beak.]

There you are. Your brother will wake up if you give him this. I won't charge this time, since he was merely the victim of incidental mischief.