Yes, in stringhalt, the abnormally high picking up of the hind will be followed very quickly by the hoof slamming back down to the ground. It has the appearance of being an involuntary plopping back down, almost as if the limb is on a rubber band. Shivers has varying degrees of severity (I had a horse in the past with it and have one now also) but usually once the hind leg is picked up, it will either stay up and stationary, with the horse unable to relax the muscle and lower it no matter how hard the human tries, or there will actually be some quivering ‘shivering’ in which there is a tremor seen in the haunch muscle. Both of these can be triggered by backing up, but can occur any time the horse is asked to pick up its hind hoof. As shivers is one of the things that responds pretty well to dietary support, keep in mind the horse needs a low/lower starch and sugar diet and higher fat than the average commercial feed. One article I found about it online actually mentions two particular brands of feed but I do not know if it is OK to list those here.