I have not yet had the experience of shapeshifting. I am thinking that what is being referred to here is something like a figure of speech, or a metaphor. Language is being used to convey a particular message. The writer may be referring to an emotional rather than a physical state; maybe an abstract state like happiness or ecstasy which could be described in very abstract terms. In some cases like animals it is a little harder to be sure what is going on. Animals may appear to us as spirits or messengers, either in real life or during meditation or pathworking. These may be messages from within or messages from outside oneself. The animal forms might represent something like this; in terms of other forms, something like a string on a harp can make sounds, sounds are energy vibrations which can cause change and can be used purposefully within a ritual context to create changes of consciousness. One might experience sound as a message or signal within meditation or a sacred context; say with the sound of a harp string. or almost any other instrument. the writer then is trying to describe this experience. this is just an opinion of course. within other planes of being shapeshifting may be easier and more literal.