Commentaire sur Les Psaumes 144:8

Whose mouth speaks vanity, etc. Scripture connects vanity with the mouth and falsehood with the right hand. When they come to tell with their mouth, they invent exaggerations of vanity, even to misrepresent what is known. If they come to stretch forth their right hand to swear, they refrain from vanity, lest they be caught as thieves, but they do swear falsely, for so is their lot.