The reasons why cats keep staring at the door in the middle of the night:
1. Cats have very keen hearing. When they feel the sound of a mouse, they will keep staring in the direction of the mouse. .
2. Cats have very strong night vision and can see dim light that is invisible to human eyes. If a cat keeps staring at the door, it may be attracted by the light.
3. When a cat first arrives at a new home and feels uncomfortable in the new environment, it will keep staring at the door to learn about its surroundings.
4. When the cat is not in the same space as its owner and is very dependent on the owner, it will always stare at the door of the owner's room.

5. When someone passes by the door and the cat hears the sound, it will keep staring at the door curiously.