What have we to do with thee? (ti hmin kai soi?) The same idiom in Matthew 8:29 . Ethical dative. Nothing in common between the demon and Jesus. Note "we." The man speaks for the demon and himself, double personality. The recognition of Jesus by the demons may surprise us since the rabbis (the ecclesiastics) failed to do so. They call Jesus "The Holy One of God" (o agio tou qeou). Hence the demon feared that Jesus was come to destroy him and the man in his power. In Matthew 8:29 the demon calls Jesus "Son of God." Later the disciples will call Jesus "The Holy One of God" ( John 6:69 ). The demon cried out aloud (anekraxen, late first aorist form, anekragen, common second aorist) so that all heard the strange testimony to Jesus. The man says "I know" (oida), correct text, some manuscripts "we know" (oidamen), including the demon.