The action is similar to a beg with the paws resting on the chair. Dog should stick nose down to the treat between paws. You may find this easier to do on a low table. While standing behind dog, guide paws on to table and encourage him to lower muzzle between paws towards the treat. While the larger dogs are in bow position, the small one starts at one end and walks under their rear legs.
Trick is to keep the large dogs from lying down.
This takes great concentration and muscle control by the large dogs. Trick is to get her to do it on command and from distances. First decide on a hand signal that is not similar to any other. I think this looks more like a mouth opening and closing. Other handlers use a closed fist, twisting motion.