Free Centaur Aisle by Piers Anthony

the Hoofer dangerous?"
    "Not if you have the wit to stay out of her way."
    "I've got to climb to the top of this slope."
    "Extraordinary fortune," the glass said brightly.
    "What?"
    The glass sighed. "I keep forgetting that animate creatures can not match my brilliance. Recognizing your handicap, I shall translate: Lots of luck."
    "Oh, thank you," Dor said sarcastically.
    "That's irony," the glass said.
    "Irony—not glassy?"
    "Spare me your feeble efforts at repartee. If you do not get moving before that cloud arrives, you will be washed right into the sea."
    "That's an exaggeration," Dor grumped, starting back up the slope.
    "That is hyperbole." The glass began humming a tinkly little tune.
    Dor made better progress than before. He was getting the hang of it. He had to put his feet down flat and softly and will himself not to skid. But the Sidehill Hoofer came charging around the cone again, spooking him with a loud "Moooo!" and Dor slid down the slope again. He was no more partial to this bovine than he had been to Irene's sea cow.
    The cloud was definitely closer, and playful little gusts of wind emanated from it. "Oh, get lost!" Dor told it.
    "Fat chance!" it blew back, ruffling his hair with an aggravating intimacy.
    Dor went up the slope a third time, by dint of incautious effort getting beyond the slight gouge in the mountain worn by the Hoofer's pounding hooves. The glass hummed louder and finally broke into song: "She'll be coming 'round the mountain when she comes."
    Sure enough, the Sidehill Hoofer came galumphing around again, spied Dor, and corrected course slightly to charge straight at him. Her uneven legs pounded evenly on the incline, so that her two short horns were dead-level as they bore on him. Blunt those horns might be, but they were formidable enough in this situation.
    Oh, no! It was no accident that brought this creature around so inconveniently; she was trying to prevent him from passing. Naturally this was the third barrier to his entry into the castle.
    Dor jumped out of the way and slid down to the brink again, disgruntled. The Hoofer thundered by, disappearing around the curve.
    Dor wiped another dribble of slime off his nose. He wasn't making much progress! This was annoying, because he had passed his first challenge without difficulty and faced only two comparatively simple and harmless ones—to avoid the Hoofer and scale the slippery slope. Either alone was feasible; together they baffled him. Now he had perhaps ten minutes to accomplish both before the ornery raincloud wiped him out. Already the forward edge of the cloud had cut off the sunbeam.
    Dor didn't like leaning on his magic talent too much, but decided that pride was a foolish baggage at this point. He had to get inside the castle any way he could and get Good Magician Humfrey's advice—for the good of Xanth.
    "Glass, since you're so bright—tell me how I can get past the Hoofer and up your slope before the cloud strikes."
    "Don't tell him!" the cloud thundered.
    "Well, I'm not so bright any more, now that I'm in your shadow," the glass demurred. This was true; the sparkle was gone, and the mountain was a somber dark mass, like the quiet depths of an ocean.
    "But you remember the answer," Dor said. "Give."
    "Take!" the storm blew.
    "I've got to tell him," the glass said dolefully. "Though I'd much rather watch him fall on his as—"
    "Watch your language!" Dor snapped.
    "—inine posterior again and dip his nose in the gunk. But he's a Magician and I'm only silicon." The glass sighed. "Very well. Cogitate and masticate on—"
    "What?"
    "Give me strength to survive the monumental idiocy of the animate," the glass prayed obnoxiously. The cloud had let a gleam of sunlight through, making it bright again. "Think and chew on this: who can most readily mount the slope?"
    "The Sidehill Hoofer," Dor said. "But that's no help. I'm the one who—"
    "Think and chew," the glass repeated with emphasis.
    That reminded Dor of the way King Trent