My kid and I have a running head-canon that cats are actually higher-dimensional slug monstrosities that our human brains can't fully comprehend.
The "cats" we know and love are actually an anglerfish-like protrusion that pokes through into our lower-dimensional spacetime.
The saliva they coat themselves in contains a mild hallucinogen which produces a calming effect that helps mask their true natures, so they can lure humans closer to feed off the kinetic energy of headpats.