Funnily enough I downloaded some stills of this class act, Miniatures Perfect, a few weeks ago, and can't get enough of this fabulous couple.
The only thing that could improve the vids would be seeing the looks of pleasure 
and ecstasy 
on their faces . . .
This couple obviously know, either consciously or sub-consciously intuitively, that a light slow touch across the skin is the most erotic possible.
It's all to do with receptors in the skin that are designed/evolved to respond with pleasure to being "touched /stroked" at a speed of 2.5 centimetres per second,(one inch/sec.).
The receptors are called, for further research,
C-Tactile Afferents
There's a BBC article in plain English here, either watch the vid or click "Open Transcript" to read text: