Yon Ill Wind by Piers Anthony

if Chlorine hadn't thought to ask, they would have fallen into the trap.  What would Nimby have done then?  Maybe he would have reverted to his dragon form and carried her away to safety—if Chlorine asked him.  But the rest of them would probably have been out of luck.
    Chlorine must have had a similar chain of thought.
    “Nimby-—I have undertaken to guide these folk safely out of Xanth.  If anything happens to them, I will have failed.
    I wouldn't like that at all.  So please warn me if anything threatens them, as well as me.  I mean, if it threatens them without threatening me, warn me, because that's part of me too—the decent part.  If they are hurt, I will hurt too.”
    Nimby nodded.
    “Thank you,” Jim said.
    Now they were approaching the volcano.  Smoke was issuing from its aperture.  “Is that thing active?” Jim asked.
    “Yes, that's Mount Pinatuba,” Chlorine said, peering ahead.  “The last time it got angry, it blew out so much dust that it cooled all Xanth by a degree.  But it doesn't blow its top if you don't insult it.”
    “Volcanoes care?” Sean asked.  “How can they, when they aren't alive?”
    “Don't speak loudly,” Chlorine cautioned him.  “It might hear you.”
    Indeed, that seemed to be the case, because the mountain shuddered and blew out a plume of gas.
    “Oh, I didn't mean to disparage it,” Sean said quickly.
    “I think it's a pretty impressive volcano.”
    The mountain subsided, and the plume drifted away in the wind.
    “Everything cares,” Chlorine said.  “The inanimate can be very sensitive to slights.  King Dor can talk to it, and it answers him.  Most things aren't too smart, but they do have opinions.  So we have to be careful not to insult them, unless we have reason.”
    “I guess so,” he agreed, clearly impressed.
    “Mom, can I use the privy?” -Karen asked.
    “It's full,” Mary replied.  “We need to stop where we can empty it.”
    She was right.  The storm had confined them pretty much to the RV, and they hadn't been able to attend to certain details.  “Chlorine, is there a rest stop along this road, nearby?  One that isn't goblin-infested?”
    Chlorine consulted with Nimby, who nodded.  Soon he pointed to the side, and Jim swung onto an exit road.  Sure enough, it led to a pleasant glade with a house in the center.  He pulled up beside the house, and paused.  “This is safe?” he asked Nimby.
    The young man hesitated, then nodded.
    The others opened the side door and piled out.  But Jim delayed.  He hadn't liked that hesitation.  “Is there something you're not telling us, Nimby?”
    Chlorine had gotten out with the others, so they were now alone in the vehicle.  Nimby hesitated again, then began to write a note.
    Jim waited, and in due course read the note:  Danger is looming close.  Your family will learn it at this site, and be alarmed.  This will make your journey more difficult.
    “What danger?”
    The storm is stirring up bad creatures.  They will frighten your children.
    “But we will escape unharmed—if we follow your advice?”
    Nimby nodded yes.
    “Thank you.” Jim hesitated, then spoke again.  “I wish I could know more about you.  Nimby, but I hesitate to inquire.  Maybe some other time.” Then he, too, got out of the vehicle.
    The region was very nice.  Karen had found a tree, and was picking a pie from it.
    Jim stopped, doing a double take.  A pie tree?  Yes, so it seemed to be.  So it really was true:  pies grew on trees, here in the magic land of Xanth.
    He went to the facilities, which were somewhat primitive but usable; what more was to be expected of trolls?
    The wind whistled through the cracks; there was no doubt the storm remained near.
    Then he thought of the pets, and returned to the RV to see to them.  He found Nimby communing with them, though they were normally somewhat shy with strangers, they seemed completely at ease with the odd young man.
    As Jim approached.  Nimby