Metal ion, an astonishing illusionist: In a new concept, “illusionary” polymerase activity is intentionally triggered at T–T and C–C mismatched primers by Hg2+ and Ag+ ions, respectively. A novel strategy to construct molecular-scale logic gates utilizes the nonnatural polymerase activity induced by the metal ions by rational design of the primers and selection of the type of DNA polymerase (see picture).