The jockey saw the horse groom sprinkling something behind his horse's neck.
"What's that?" asked the jockey.
"It's yeast", answered the groom. "This will discourage birds from mistakenly building nests in your horse's beautiful mane."
"Will that really work?" asked the jockey.
"Of course!" replied the groom, "for yeast is yeast and nest is nest, and never the mane shall tweet."