In plain words
The third is madhyama mudrā. That is, we must place our gaze midway between the nose and the point between the brows. When the gaze rests on the tip of the nose, our eyes do not look open even though they are open. So when we do bhūcarī mudrā on the tip of the nose, there is no need to close the eyes. But while practising madhyama mudrā, the eyes must be half-closed. That is, when we look at the tip of the nose, with half-closed eyes it narrows still further.
Then ṣaṇmukha mudrā. It is very sacred. It is hard. We must close our two eyes, our two ears and the two openings of our nose, and keep our gaze at the point between the brows. That is, closing the two ears and closing the two eyes: this is ṣaṇmukha mudrā. With the two eyes, the two ears and the two nostrils all fully closed, we must take a breath once in seven minutes. If we practise this way for a month, it gradually becomes a habit. We will feel no strain or discomfort in the breath at all. By doing this, both the mind and the senses turn inward. What is its inner meaning? Simply through hearing the many kinds of sounds of this world, our mind goes through more agitation, or delight, or some middle way between the two.
When our eyes see certain things, certain matters, certain people, the mind likewise goes through agitation, delight or a middle way. In the same way, when we smell a stench or a sweet scent, the thought "Where is the thing that gives off this stench or this scent?" troubles the mind still more. So its inner meaning is that when we hold back sight, sound and smell, the mind turns inward. But today our hearing, our eyes and our sense of smell are forever spreading out over the world. When someone somewhere is talking under a tree without our knowing, we slip in there quietly, eager to hear what they are talking about. Simply through our hearing those sounds, the distortions of the mind grow even more. When some new person has come, going up to him, talking with him and asking after his welfare and his circumstances is a bad habit of ours.