I thought cannibals shake after eating too much human meat.
Though that could just be from 'The Book of Eli'...
I think the Book Of Eli is using the disease Kuru to draw inspiration:
http://en.wikipedia.org/wiki/Kuru_(disease)
It is also thought that cannibalism was quite common in our distant past:
http://news.nationalgeographic.co.uk/news/2003/04/0410_030410_cannibal.html
This raises an interesting question for me, as I always held the opinion that we have an innate mechanism through thousands of years of evolution so that we dont wipe our own species out by eating each other!