The narrator may be unreliable for many reasons. Some of the typical scenarios are: The narrator may be of a dramatically different age than the people in the story, such as a child attempting to explain adult actions. The narrator may have prejudices about race, class or gender. The narrator may have low intelligence.
Thus, proteins containing these amino acids would be made up of very small amounts of sulfur, in addition to the more common elements listed above. The five chemical elements of protein are, 1.) sulfur 2.) carbon 3.) hydrogen 4.) oxygen 5.) nitrogen.
In other words, all the amino acids that you have making up all of your proteins are the L form, L-serine, L-proline, etc. It is also of interest to mention that there are several biologically important amino acids not found in human proteins.