Thank You

In the office, today, someone I did not know well enough to call my friend gave me a huge chocolate bar.
I said "thank you," but couldn't resist asking, with a puzzled smile "why?"
She said "because you have been nice to me. Thank you so much."
I felt strangely touched, both by the gesture and the answer to my question.
I was reminded that kindness, when given without expecting to be returned, is almost always sure to come back.