Here's why it's difficult:
* Phonetic vs. Spelling: Palindromes usually rely on spelling. The sounds of "horn" and "sound" are similar, but their letters are different.
* Meaning: A true palindrome should have the same meaning forwards and backward. It's hard to maintain the meaning of "sound of horn" when reversing the letters.
Possible options, keeping in mind they're not perfect palindromes:
* "H-O-R-N S-O-U-N-D": This is technically a palindrome if you consider the letters, but it loses the original meaning.
* "R-O-H N-O-U-D S": Similar to the above, this is a palindrome of letters but not of the meaning.
Let me know if you'd like to explore other wordplay or create a different palindrome!