This is simply a conditioned response of the nervous system to stress in some animals and is not related to hunger but rather heightened emotion. This is something more unique to the dog than experienced with human beings, but there can be other similar consequences of stress in both species, for example, trembling, becoming weak in the knees, so to speak, and exhibiting nervous behavior, even possibly losing bladder or bowel control in extreme circumstances. Unfortunately, some dogs are more sensitive than others to certain stimuli and this can be a challenge for them when the lifestyle of their human companions puts them seemingly in harm’s way by subjecting them to situations not to their liking. Sometimes this can be overcome through training and special steps taken to desensitize the animal to the adverse stimulus to render it tolerable. It is always worth the attempt rather than to simply leave the animal to its own devices so it suffers on a chronic basis entirely on its own.