The theme is sex ... LOL
Well basically, the illustration, shows pleasure, energy and connection, at least at this time the two people were well understood ..
The pleasure and power, I pass by the colors, besides the water (it has 2) and hair that make fire and expression (body and face). Ah yes! the man also gave the idea of energy, the pose and showing a little muscle.
The connection is also shown by the sheets, which roll in the two lower.