He thought he saw some horses, too, and a clown, but it was the faces of all those dead raptors that really bothered him. And maybe that clown a little bit.

I'm not saying the plot doesn't have holes.

Jeez, Hazel," Percy said, "tell your horse to watch his language."
Hazel tried not to laugh. "What did he say?"
"With the cussing removed? He said he can get us to the top."
Frank looked incredulous. "I thought the horse couldn't fly!"
This time Arion whinnied so angrily, even Hazel could guess he was cursing.
"Dude," Percy told the horse, "I've gotten suspended for saying less than that...

A cavalryman's horse should be smarter than he is. But the horse must never be alowed to know this.

Alright. You hate me, I'm not too fond of you. It's mutual..." he muttered, walking hesitantly toward the stallion, hand outstretched, "I know you want to bite my hand off, but I swear I have no carrots, so you have no excuse. You want to throw me when I get on you...but if you even try, I will stab you.

He flung himself from the room, flung himself upon his horse and rode madly off in all directions.