Based on Swertyd's suggestion of *convinced* horses (see Horse Drug Silliness Post): More suited to radio.
F/X: BACKGROUND SOUNDS OF HORSES AND TRAINERS
ANNOUNCER:
Calling all competitors for Eventing to make your way to the arena.
HORSE 1:
At The End Of The Day, you've got no chance. I'm gonna clear every fence, easy peasy. I'm the greatest horse that ever lived!
AT THE END OF THE DAY:
That's A Good One, how can you possibly think you can beat me? I'm not a common horse like you, but a majestic unicorn. Books have been written about how I'm the only pure creature. Be awed at my silver coat, and my horn of invincibility.
THAT'S A GOOD ONE (Horse 1):
I'm afraid you have confused me with your usual riff-raff. For I am Pegasus, and my wings will help me soar over all the fences - including the really garish purple house one. You don't look like a unicorn to me - your "horn" looks a bit like a boil.
AT THE END OF THE DAY:
That's rich coming from "Mr. Bingo Wings!"
THAT'S A GOOD ONE:
Imbecile! You will pay for your insolence! At The End Of The Day, I'll make you change your tune!
HORSE 3:
Young horses these days. Ay, Brutus, are there any left who will not succumb to employing foul means, using drugs to win?
BRUTUS:
Moooo!?
HORSE 3:
Et tu, Brutus?