viretarmis,

But the use of the pillow suggests that the couple knew perfectly well what they were doing, and they had planned it. If they were completely mentally insolvent, they would've engaged in public displays without the self-consciousness implied by the pillow.

Although you say that the elderly would have had inhibitions about public displays when they were young, when old people lose their inhibitions, it means that they're simply engaging in behaviors that they might have wanted to do if self-consciousness hadn't prevented them. Also, I'm sure that at least some of our (grand)parents weren't so chaste as they'd have us believe! After all, would we listen to their abstinence messages if they told us about their first tryst in the backseat of the Galaxy in the park?