Smile curve

In some of my recent meditation sessions, I had an interesting observation.The initial part of the meditation process is always relaxation.When I relax my facial muscles, I observed that, a slight
smile automatically sprouting. My observation is that, when facial muscles settles down in the relaxed state, it automatically settles in a with slight smile.I didn't conciously create the smile; but it comes, thats the way the face will be when we are relaxed and meditative.This smile I have seen in the face of great gurus.When realized it for the first time, it was like a revelation..