up. this will be easier if he or she can stand on command.
hold a treat at the tip of the dog's nose and move it down slowly while saying "take a bow." hold it close to the dog's body and lure him down until the elbows are on the floor.
hold the bow for a couple of seconds and use the treat to lure the dog back to standing.
as soon as the bow is complete, praise the dog and give the treat.
practice several times a day, no more than a few minutes at a time, and before you know it, the command "take a bow" will make your dog bow.
if your 