I just read an amusing article published in Clinical Infectious Diseases, a medical journal published by University of Chicago, in 2006. The article is titled "'Strange things I have in head': Evidence of Prion Disease in Shakespeare's Macbeth". You can access it (I hope) at http://www.journals.uchicago.edu/CID/journal/issues/v42n2/37985/37985.text.html
The article purports to show that Macbeth may have acted the way he did because he was suffering from a disease. Prion diseases (formerly known as slow-virus diseases) are a collection of neurologic diseases affecting humans and animals. The three human forms are Familial fatal insomnia, Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease. This last one is considered the human form of bovine spongiform encephalopathy, more commonly known as Mad Cow Disease.
The article in question uses multiple quotations from Macbeth to show that Macbeth may have been suffering from variant Creutzfeldt-Jakob disease . The article is well written and contains a really good table (which can be accessed from the web page above-click on Table 1 in the text of the article) with all of the quotes and which of the prion diseases the quote fits best.
I really love this kind of fun with Shakespeare. It just shows how much there is to find in there.