"No, don't apologize", Valerion said, a great smile on his face. "You did amazingly. Don't worry about the fire; you are safe in this tower".

Adrien watched the last bits of the paper ball turn into ash and sizzle away. Then he realized: something had been different about this last attempt - unlike the bat and the wall, the fire had been perfectly visible; and now that he was thinking about it, he recalled that, for a split second, he thought he had even seen the fireball fly towards the paper ball before it touched it and ignited it. "Ah -- Valerion", Adrien began, "was there a visible fireball, or am I just imagining --?".

"No, I saw it too", he answered. "You did make a fireball".

"But then -- how come this fireball was visible, but the bat and the wall were invisible?".