"Except in very rare cases, it's a tool that can be wielded if one is so gifted." As he mentions the word 'tool', there is an image of a large, shallow dish held up on fine wrought-metal tripod and filled with molten silver. The liquid moves under its own power and ripples, distorting any images that Mycroft might be able to see. As it is, there will be brief, choppy split-second single frames related to Harry's time learning occlumency.