The cat's scratching at the door is probably driven by curiosity. For an active cat, every time he sees something behind the door, he wants to go in and have a look.

To solve this problem, you can try the following measures:

1. Accept the cat's curiosity: let the cat know that if it feels lonely or bored, it can come to your side at any time, or you will play with it at any time, providing it with new stimulation and guiding it to get rid of the habit of scratching the door.

2. Provide toys for cats: Cats usually like toys such as balls, ropes and small hooks. Provide some rich toys for them to play in the room. At the same time, keeping toys fresh and interesting will make cats less bored.

3. Gradually exercise the patience of the cat: play with the cat more, gradually increase the play time, and let the cat wait patiently for the next play time.

4. Set up different cat areas: Set up a specific place for cats, such as nests and cat trees, where they can play, crawl and stare at animals to maintain their curiosity and excitement.

5. Change the olfactory environment of animals near the door: In some cases, cats may think that there is a threat behind the door, such as other animals or strangers. So you can keep the smell fresh behind the door and let the cat know that this is a safe area.

Generally speaking, it takes patience and time to change the behavior of cats and gradually establish good habits and behavior patterns. Keep a step-by-step pace and attitude, and don't disturb their needs and personalities, so as to establish close ties with them.