The Abhinaya Darpan mentions that the dancer should sing the song by the throat, express the meaning of the song through hand gestures, show the state of feelings by eyes and keep track of the time with feet.
From the Natya Shastra, a text on the arts, this beautiful quotation and translation was often quoted by Indian classical dance instructors:
"Yato hasta stato drishti"..."Where the hand is, the eyes follow"
"Yato drishti stato manaha"..."Where the eyes go, the mind follows"
"Yato manaha stato bhava"..."Where the mind is, there is the feeling"
"Yato bhava stato rasa"..."Where the feeling is, there is mood"
So vast is the hand gestures that it covers almost all the aspects of human life and the entire universe.
Hence 'Mudras' form a distinct code language and bring unique poetic element while performing abhinaya and thus the language of the mudras enables the dancer to express practically anything and everything.