It is unfortunate in some ways that so much emphasis is given to the outer aspects of mudra as the inner meaning can be very difficult to locate from here.
Mudra is the deepest tool within the traditional techniques of yoga to connect us all the way through the continuum of our being. And every mudra works slightly differently to emphasize a different aspect of our opening into fullness.
Shambhavi mudra begins like the stem and then opens into the flower of clarity.
Many of the mudras like the traditional bandhas, the Vajroli, and the Yoni mudra also work with the central nadi and act like a river leading to the opening of the mouth of the ocean.
The Pasa mudra, extremely powerful and simultaneously tricky, works with the desire and expands into bliss.
These mudras work in some way first with contraction or narrowing that expands later into vastness.
Other mudras like Khecari expand us directly into space.
Each mudra works with an aspect of our limitation and reveal the deeper face of what that limitation actually is.
Many in the beginning feel confused by these subtle techniques. It is important to know where to enter. The space of transition is very powerful as it is here that a deeper window opens up to us. This is why the traditional pranayama and khumbhaka (retention) have been given first in the texts, to teach us to enter these transitions. The bandhas are a good place to start. The simple transitions in our life are also powerful.
Mudra occurs itself as a transition. A transition from the objective rational world to the instrumental world of the sensory. The transition may also affect us in such a radical way that it drops us directly down to the subjective level or even below that to the radiance of our natural state. The instrumental and subjective layers of our being are vast continuums themselves and the mudra can help us cross this large landscape in a powerful mode of exploration.
When you begin to really explore this level of mudra it is like entering a river and trusting it to take you. You start to learn how to feel it out and it speaks to you, calling you, correcting you. It is dialing into the deepest core of your being and as you follow this river, many things around and in you change or transform. It is very organic.
There are other mudras, many, some of which I am only beginning to see. This world is vast. The instrumental layer of our being is vast. It is a landscape of great beauty. Navigating this landscape feels like swimming in a deep full ocean of incredible wonders.