The word "hoarse" makes this statement into a pun. A pun is a form of wordplay that relies on multiple meanings or similar sounds of words to create humor. In this case, the word "hoarse" sounds similar to "horse," which is a type of animal. The sentence suggests that the pony is quiet because it is a little hoarse, which has a double meaning: the pony is both quiet and has a raspy voice (like being coarse or hoarse). This play on words creates the pun.
