Don’t know any better
This phrase means “someone does something bad or stupid because they have not been told or taught that it is wrong”
1. You should use nonstandard English only when you intend to, rather than fall into it because you don’t know any better.
2. One person correctly thinks of a “vocal cord” as a part of the anatomy, and another “hears it” as “vocal chord” meaning a sound. So, they will add the second, incorrect spelling and interpretation as acceptable just because a lot of people don’t know any better.