This is a very interesting symbolism- blood represents life, the very life force that flows thru the entire cosmos. Her blood stained tongue which is stained by drinking the blood of a demon (ignorant being- i.e. ego) shows that Kali can take away the very life-force of darkness and ignorance, so they are brought to nought! Using the chopper, she cuts off the head of the ego (false, ignorant, and deluded self) to liberate the soul from ignorance into her bliss of Divine presence and Truth. In this regard, Kali is the mother who creates all of creation. With respect to the parts which are caught in the delusion of separateness (Maya), she acts as the loving mother who annihilates the delusion and makes her child whole again- allowing them re-birth into her very being- as their higher, divine self.