While assisting humans, I have found that there is a correlation between emotions and organs of the body. Anger and resentment affect the liver. Fear affects the kidneys. Grief affects the lungs and heart. Worry affects the stomach.
Animals pick up on our feelings and the energy in their bodies are affected. When communicating with them, whether in person or by looking at a photo, how they are feeling physically may be a reflection of their human companion's emotional state.
When you are stressed, depressed and experience fluctuating emotions, your pet senses this and also may feel the tension. Taking care of your emotional wellbeing will help your pet to be happier and healthier.