To add to this, the "walking in place" animation happens when Mario's position + velocity would end up out of bounds, which the game doesn't generally permit. W

To add to this, the "walking in place" animation happens when Mario's position + velocity would end up out of bounds, which the game doesn't generally permit. When the player turns and allows the speed to drop, the motion will take Mario to a valid position, and he will zoom until he gets stuck again.