Unintelligible – Impossible to understand

"Understanding intelligent people is impossible", (unintelligible) said the young student. "They are impossible to understand".

Examples of unintelligible in a sentence

Animal sounds are unintelligible to humans but we can use body language to figure out what they want.

The doctors notes were unintelligible, as usual.

I like all the music by this singer, but the lyrics are completely unintelligible.