Working with models who have had some sort of training makes it a whole lot easier for photographers to shoot them. Some can turn on the charm at a drop of the hat and for that brief moment, that's all you are looking for.
This was shot on film by the way using a 70-210mm lens with a f/2.8 aperture. Fill in flash was used as it was shot in the mid day sun. If you shot without it, there will be very harsh shadows below the chin area.