It is said that during the First World War, a French pilot, flying at an altitude of 2000 meters, found a "bug" next to the plane flying at the same speed.

Because the pilots of high-speed aircraft fly with bullets, the position of bullets relative to the aircraft has not changed.

So the bullet is stationary relative to the plane, which is why the pilot of the plane reaches out and catches the bullet;

At this moment, taking the plane as a reference, the bullet remains motionless. If the ground is really taken as the reference object, and their positions relative to the ground have changed, then both of them are moving with the ground as the reference object.

So the answer is: still; Airplane.