3D porn is a trend in the late 70's and early 80's that was a desperate attempt to save the soon to be extinct porn film(in contrast to the porn video). These awkward, expensive skin flicks instituted the Red/Blue stereoscopic technique and commonly 'featured' John Holmes. 'Featured' was commonly justified by adding a single disjointed scene of stock footage of John in action. John Holmes last film Hard Candy was, in fact, one of these.