The 3rd Earl of Salisbury, was around in England in the 13th century, fighting mostly. He's buried in Salisbury Cathedral. A dead rat was found inside his skull; the rat was tested and found to contain traces of arsenic, which some have claimed suggests that Longespee was poisoned. Possible, but having a rat wandering around inside your head isn't going to be very good for you either.
Here's his tomb. The rat is preserved in the red box. The windows in the background commemorate the Army Air Corps (which still exists) and the Glider Pilot Regiment (which doesn't).
