A union in physical love is called gentle if it is performed with a soft lingam - i.e. without an erection. This is possible in the so-called scissors position, as I showed you in the video recently.
A silent union means that the husband and wife are in silence or at rest with one another. The lingam can also be erect. It is a tantric practice not to become active, but to remain meditative and pay attention to the subtle energy flows inside the body.
Soft and silent meditations can alternate one after the other as desired. And the lovers watch the whole thing without engaging in normal sexual activity.