He's right, it's there, at about 1:27 in this clip.
CNN was airing Vice President Dick Cheney's speech live from the American Enterprise Institute in Washington -- when a large black 'X' repeatedly flashed over the vice president's face! The 'X' over Cheney's face appeared each time less than a second, creating an odd subliminal effect.
UPDATE: Just a glitch. But an interesting "glitch" none the less.