When the momin progresses through firm faith and certainty and reaches the level where the light of faith becomes rooted such that it becomes similar to the instinct in animals, then he becomes a complete wali (saint). The animals (hayawan) do not accept any outward interference in their constitution, either from their surroundings or from desires, therefore they are truly alive (hayy + wan)……. it is for this reason that they hear the sounds of those being tormented in their graves; whereas human beings do not for they have not yet reached the station of being truly alive. “And verily the life of the hereafter is the true life”.
An-Nahl, Pg 94.