Writes at length on the origins and meanings of particular head movements as used to express assent or disagreement, especially the sideways movements of the head as an expression of consideration or contemplation.

Also discusses space and colour perception.

Speculates on the function of eyebrows and of hair and the furrows of the forehead. Considers many features and faculties to serve, or to have served, more than one function, either simultaneously or successively. Determining the one function through which natural selection has acted in developing it is unrealistic and not worth while.