The goal with all stretches is to use treat(s) to lure, talk softly, encourage as much duration as you can (usually is only -3 seconds), and encourage SLOW calm graceful movements. At first terriers really struggle staying calm (heck who am I kidding Miles and I still are working on this often!)
Above: Miles stretching before a run at AKC Invitationals in December of 2019 in Orlando. These stretches are all professional canine athlete worthy! 😜