The art work titled "Inside Voice" is an abstracted interpretation of the human ear.  You can see the ear canal, the ear drum, the anvil and stirrup and even the cochlea (a coiled tube that looks similar to a snail).  This is the physical process of what happens when sound enters our ears.  In this case the ear is receiving the sounds from oak leaves that are moving in the wind.  In Greek mythology, for those who knew how to listen, the sounds of oak leaves were thought to be the voices of the gods.