What the hell did that lecherous daughter slip into her father's tea, some kind of stimulant? She deliberately wanted him to get a hard-on, and she walked around the house in her panties! And where could the man go when his head had already caught the target. No dick could resist that temptation.
It's a turn-on when you look at a young, beautiful couple. The girl couldn't take it either and decided to keep up the company, with everyone enjoying themselves each in their own way. Beautiful sex.