The holes on the interior surface are steam holes, which can conduct water vapor to the thermostat at the bottom of the kettle and trigger the thermostat to cut off the power. It is a normal structural design, so please feel free to use it.
Note:
Most of the mechanically designed kettles on the market have similar holes on the interior surface. These steam holes are essential for maintaining the kettle's operational integrity. It should not be covered or blocked to ensure proper functionality and lifespan.