In the Viennese Oyster position the receiver lays on their back with their lower back and legs raised all the way up so that their ankles are crossed behind their own head. The exact end position will depend on the flexibility of the receiver. This position totally exposes the groin area to the giving partner who lays atop the receiver to perform. The giver moves up and down on the receiver to create friction. The giver needs to use their hands to support their own body weight so as not to crush the receiver.
This position requires considerable flexibility on the part of the receiver and it cannot be (fully) achieved by most, but it is wonderfully "naughty" due to the feeling of being totally exposed. Those less flexible might try getting into the position, but stop at the point where the position starts to become uncomfortable. The giver can also help those less flexible by using their hands to support the receiver's thighs at mid-point.