Often it's the dynamics of the situation that are the most thrilling.

The dynamics of the situation are the most thrilling part.

If you compare the aroused yet restrained penis of the husband with the free and erect cock of her boyfriend you’ll find they seem roughly the same size, yet his wife is eagerly servicing her boyfriend with her mouth in anticipation of having that cock inside her. This demonstrates the mental component to the lifestyle where the thrill of denying her husband and enjoying another in front of him are easily as thrilling as having a much larger cock. In fact, it could be said that choosing another male with a cock no larger than her cuckold’s penis is a better exercise of D/s in that the wife enjoys teasing and denying her husband perhaps even more than the extramarital intercourse.