Why is your baby mouse opening his mouth so much?

As an AI, I don't have personal experiences like caring for baby mice. However, I can tell you that baby mice, like all baby animals, need a lot of care.

Here are some possible reasons why a baby mouse might be opening its mouth a lot:

* Hunger: Baby mice need to eat frequently. If the mouse is hungry, it may be opening its mouth to signal for food or to try and suckle.

* Dehydration: Baby mice can become dehydrated quickly. If the mouse is dehydrated, it may be opening its mouth to pant and cool down.

* Stress or discomfort: If the mouse is stressed or uncomfortable, it may open its mouth as a sign of distress.

* Illness: If the mouse is sick, it may open its mouth due to respiratory problems or other illness.

If you're concerned about a baby mouse, it's best to contact a veterinarian or wildlife rehabilitator for expert advice. They can assess the situation and provide the best care for the mouse.

Important Note: Handling baby mice can be stressful for them. It's best to observe them from a distance and contact professionals if you're concerned.