Where there is duality one sees another, smells another, tastes another, offers respect to another, hears another, thinks of another, touches another, and is aware of another.
yatra tv asya sarvam atmaivabhut tat tena kam pasyet, tat tena kam jighret, tat kena kam rasayet, tat kena kam abhivadet, tat kena kam srinuyat, tat kena kam manvita, tata tena kam spriset, tat tena kam vijaniyat
But for one for whom the Supreme Self is everything, how can he see another? How can he smell another? How can he taste another? How can he offer respect to another? How can he hear another? How can he think of another? How can he touch another? How can he be aware of another?
From Brihadaryanika Upanishad: 2.4.14:
Unanimous Tradition / Tradición Unánime 