1. Darwin C. The expression of the emotions in man and animals. Oxford, UK: Harper Collins/Oxford University Press; 1998. (originally published in 1872)
2. Fridlund AJ, Gilbert AN, Izard CE, Burdett AN. Emotions and facial expression. Science. 1985;230(4726):607–8.
3. Ekman P, Friesen WV. Constants across cultures in the face and emotion. J Pers Soc Psychol. 1971;17(2):124–9.
4. Ekman P, Rosenberg EL. What the face reveals: basic and applied studies of spontaneous expression using the Facial Action Coding System (FACS). New York: Oxford University Press; 1997.
5. Masson JL, Patwardhan MV. Aesthetic rapture: the rasadhyaya of the natasastra. Pune, India: Deccan College; 1970.