If you are looking for a quick solution to testing for gibberish inside a comment box without external links and which just works though not perfect,

1. Check that the text box contains at least 10 words.

2. Check that each word does not have 4 consonants or vowels in a row, but consider y as a vowel (some people consider y as a semi-vowel)

3. Pass the test if 80% of the words meet the criterion

So rhythm becomes a valid word. Applying the 80% criterion and not allowing short comments will ensure that this solution will be quite robust for most purposes.