Answer from Dr. Richard Hawkins:

This is a very common behavior which many dog owners will experience at some point. There are many potential causes as mental, physical, and training based issues can all contribute to this sort of behavior. Unfortunately, there is not much research on the cognitive reasons behind this behavior as it can be very challenging to recreate in a laboratory setting.

In my experience, your dog may be sitting down and holding fast for a number of reasons: She may be distracted by something else in the environment, uninterested or even afraid of proceeding in the direction you were walking, or there even may be a health issue causing her some discomfort.

There are several health issues that come to mind when I hear of this in my patients. Just like humans, dogs can get gastrointestinal discomfort, or a stomach ache, from many causes such as a change in diet, stress, excess gas, or even medication, just to name a few. When we humans have stomach aches we’re just as unlikely to want to go on with our normal day.

Osteoarthritis, can also affect a significant number of the joints involved in walking, and in many cases make walking a painful experience. As dogs age, this pain can grow and lead to a planted rear end during a walk.

If it happens again, keep an eye on your dog’s breathing, any sounds she makes, and her mental alertness. If anything seems out of the ordinary, it might be a good reason to visit your friendly veterinarian.

In most cases, however, you probably have a completely healthy dog! Even though it may not look like it, she may very well just be tired out and ready to go home. You could give her a break for a few minutes and try again, encouraging her with a tasty morsel to continue. But, if she's had enough, I’d would encourage you to respect her wishes in this instance, and head home.