According to one analysis, "at frames 9306 through 9368, a person with a US
military cap temporarily pokes about a quarter of his left head into the
video." You might want to look at an .mpeg of the frames in question here
to see what you think:

http://www.aztlan.net/berg_abu_ghraib_video.htm

Not a pleasant animation, or particularly conclusive evidence, so far as I
can tell.