Actually we get this material body due to our ignorance. By ignorance we commit so many wrong things, and you have obliged to accept a certain type of body. Therefore it is a network of ignorance. Śarīra abidyā-jāl joḍendriya tāhe kāl. In that network of ignorance there are different senses, joḍendriya tāhe kāl, gross material senses. They are just like our death. Sometimes these senses are described as kāla sarpa. Kāla sarpa means the black cobra. As soon as the cobra touches—immediately dead. Similarly, if we allow this kāla sarpa to act in their own way, that means we are inviting death at every moment. Therefore those who are too much bodily attached, for them this yoga system is controlling the senses, yoga indriya saṁyamaḥ. Yoga does not mean to increase the power of sense gratification. Yoga means controlling the senses.
So the Bhaktivinoda Ṭhākura said that this network of ignorance, where the senses are like black cobra, out of all those senses the tongue is the greatest black cobra.