Your dog may show submissive behavior when dealing with a certain situation or thing causes them fear. There are some causes to this behavior that can be recognized. In some dogs it may be a fear of strangers, it may be fear of getting in trouble or other things that may cause this submissive behavior.
Fear of strangers is common among dogs. The smaller dog breeds tend to be shyer at times and submissive behavior may result. The dog may start to shake showing the fear it has being around something that is unfamiliar to them. They may show this fear by running behind you and possibly hiding under or behind something.
Aggressiveness with other animals or people may cause the dog to act submissively. If the dog is fearful of a certain tone you or someone else may use, they may hide their tail between their legs; bow their head and perhaps even start whimpering. Certain animals may show their dominance by growling or showing their teeth to your dog. These actions by other dogs may cause your dog to run or not look the other animal in the eye in reaction to the dominant animal.
If the dog is abused either physically or verbally, a submissive behavior may result. The dog may not want to be around certain people or things, run and hide or just whimper to get away from them. They may tend to stick close to one person in the family compared to others feeling more secure.
Age plays a factor in submissive behavior. Dogs that are older might be more submissive because they are not able to react as fast or move as fast. These dogs make shake more or wet themselves more in fear of what is there or what has happened to them.