You call them "mobs", but "mobs" is a quite generic term. Animals and monsters without ability to speak a language are mobs too. If we talk about NPCs = "Non-Player Characters" here, regarding the contained "character", we mean mobs which provide the ability to speak to via
/tellnpc, which will react on sentences with general answers.
Well ... did anyone ever try how a rat or clacker react on
/tellnpc Hello ... ?!