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The first step to take when teaching your dog how to crawl is to have him lie down.  This will get him in position and ready to focus on the new trick he is learning.  If your dog doesn't already know the lie down trick, consider teaching him this first before teaching him how to crawl. Have a treat ready to help your dog focus and to reward him with. Once your dog is lying down, take a few steps in front of him.  Squat down and show your dog the treat.  Keep the treat low to the ground and say “crawl.”  Your dog should start to crawl along the ground, trying to get the treat from you.  Reward your dog immediately if he crawled correctly.   Your dog may stand up and walk over to you.  If this is the case, start over from the lying down position. You should only be a few steps away from your dog at first.  Walking too far away may confuse your dog. Make sure your dog crawled correctly before rewarding him.  Your dog will repeat whatever behavior you reward. Once your dog starts to understand what the “crawl” command means, you can start to increase the distance your dog crawls.  Work gradually, taking a few steps more each time you train your dog.  This will increase how far your dog can crawl as well as reinforce the trick overall.  Always work slowly to increase the distance your dog is crawling. Practice around twice a day.
Have your dog lie down. Use the "crawl" command. Increase the distance.