During the Samudra Manthan, the toxic poison ‘halahal’ emerged out of the ocean of milk. The devtas requested Lord Shiva to help them, else the poison would disrupt the three worlds—Heaven, Earth and Netherworld. Shiva appeared on the scene and saw that the toxic poison was spreading all over the ocean. He gulped the poison and placed it in his throat thereby preventing it from descending into his stomach. The poison was so potent that it changed the colour of his throat thus he got the name “Neelkantha”.
Coming to the question—
Lord Shiva’s stomach represents the Brahmand or Universe from which the entire creation came into existence. The ‘halahal’ literally refers to a deadly poison and symbolically it is the representation of the negative thoughts and energies that lead to pain, suffering, death and destruction.
These negative energies are present in all living beings in more or less quantity, however, if these forces come to us with severity then it will lead to instant death and destruction—-the world runs due to the balance between the negative and positive energies that results in the neutralization of dire consequences.
Lord Shiva, the all renouncing God is an epitome of austerity, wisdom, purity and determination with which one can drive away all negative forces. Shiva’s Neelkantha is a symbol of the Vishuddhi Chakra that is situated in the throat and is the starting point of Udana Prana. It is a function of this Prana to purify the body of toxic substances while breathing. Purification not only occurs on the physical level, but also on the level of the psyche and mind. All problems and unpleasant experiences that we have “swallowed” and suppressed during the course of our life, continue to exist in the subconscious mind until they are faced and resolved with wisdom.