Okay...the shadow on the cave wall :
- is the shadow language, which is but a reflection of the concept that exists in the mind of the human - the object casting the shadow being the concept?
- does the light source have relevance in this pictorial? If so, what does the light source represent?
- the cave wall would represent the background against which the shadow is cast...but one would have to remember that is just one part of what makes the the shadow and it's shape
...the only way to make this accurate, I would contend, is for the mind of both people to have input into the shape of the wall...with both people creating a wall that may (or may not) be similar, but one that will always have differences.
...that wall is something that they are both going to use to communicate and create from (regardless of the other analogies within - eg. the body that casts the shadow...in this case, it would be two bodies, casting shadows back and forth, in order to communicate)
And all that said - I don't see the particular use of symbolism in this thread, though it may well help others