As new technology is showing us, it's quite possible for two people to generate extraordinary eroticism while their bodies are a continent or more apart.
Eroticism emerges first and foremost from the pleasure – in which relief plays a big part – at having our secret sexual selves, witnessed, endorsed and encouraged by a kindly other.
Even later, in the car and outside the villa when God knows he had had other things to think about, his eroticism had been hotly aroused by the sight of her indecent nakedness.