Clara quotes Proverbs and hilariously says "Let not mercy and truth forsake thee.
Bind them upon thy neck, write them on the table of your heart", the word is "tablet".
She is the only person speaking and says it very clearly, which means every single person involved in the production believed that humans were instructed to write on tables. (Which would be an excellent excuse to give teachers when kids get caught doing it at school.)
Mae manages to ruin And Then There Were None by giving away the killer, while also getting the ending completely wrong. The Mark of Cain is not a real thing, it isn't a mark someone can get or leave, and has nothing to do with the Agatha Christie novel.
Possibly Mae has confused it with the Bible or an episode of Supernatural.