The eye cannot see itself. The ear cannot hear itself. The eye, again, cannot satisfy the functions of any of the other senses, or can any of the senses satisfy the functions of any sense except its own.
न वेद चक्षुश्चक्षुष्टुं श्रोत्रं नात्मनि वर्तते। तथैव व्यभिचारेण न वर्तन्ते परस्परम्॥