Question

Once upon a time, son,
They used to laugh with their hearts
And laugh with their eyes:
But now they only laugh with their teeth,
While their ice block cold eyes
Search behind my shadow

Which part of one's face reflects one's sincere feelings and emotions?

Answer 1

heart reflects one sincere feelings and emotions

Answer 2

part of one's face reflects one's sincere feelings and emotions is 

They used to laugh with their hearts
But now they only laugh with their teeth, 

i hope this helps you