My beardies always fall asleep with their heads rested on my boobs xD. It's Kira's favorite place in the whole world. She will wiggle out of her beardie burrito to snuggle down on one of my boobs.
I've always been told it's a nice place to be, apparently even animals think so. I suppose it could also either be the warmth of the hardest working muscle being felt from beneath the skin or the rhythm of our heart beating, it calms babies why not beardies?
I like how amusing this thread is ...but it is very informative also... my opinion is the same as everyone else's....its probably a very soothing, comfortable ....with your body heat the sound of your heart, and softness of them......mine also enjoys this position...