I don't know what to do when my knife cuts the day shift on the turtle's back (pictured). Who can tell me what this is, how it happened and how to solve it?

According to the photos you provided, the day shift on the back of the razor turtle may be one of the following two situations:

1. Mold growth: If the day shift is on the surface of the turtle shell, it may be caused by mold growth. In this case, you can gently wipe the white spots with clean gauze, then dilute them with vinegar or white vinegar and clean them. Then dry the turtle shell with a dry cloth, keep the turtle shell dry, and apply potassium permanganate for treatment.

2. Onychomycosis: If the day shift is in the turtle shell, it may be a symptom of onychomycosis. In this case, it is necessary to dry the turtle, soak it in clear water for two or three times a day, then clean up the rotten place, rinse it with clear water, and then apply erythromycin eye ointment or chlortetracycline eye ointment for treatment. In severe cases, antibiotics are needed.

In either case, it is suggested to provide a good living environment for the tortoise, change the water source regularly, keep the water clean and avoid re-infection. If the tortoise can't feed itself, you can feed it calcium tablets or other vitamin supplements to help it recover. If the situation is serious, it is recommended to consult a veterinarian or professional in time.