Krishn left Vrindavan to Mathura and never returned back.

A Gopi (maid of Vrindavan) wanted to write a letter to him. She took a paper. But she could not read or write. She thought is she asked someone to write for her, it would disclose her love.

She hold the paper for a while and put it in envelope and sent that paper as it is to Krishn.

Krishn opened the envelop and was perplexed to receive the blank letter.
But when carefully checked the paper there was unmistakable message hidden in it.
When Gopi held the paper in her hand, it became extremely hot because of heat of separation from Krishn. It made the paper blackish from beneath because half burning where her fingers touched the paper. Her hot tears fell on the paper and it was a bit fused on the top. It also had black sprinkles because of kohl (kajal) that was applied to the eyes which came out with tears that spread on the paper.

Krishn read the separation pangs of the Gopi on the paper on which nothing was written at all..