Jack the Ripper letters and a fossilized rat

What do the above have in common? They are both in The National Archives safe-room and were on display to staff this morning. Other items were Magna Carta, which looks as if it has been chewed by a rat, a letter from the Princess Elizabeth to her sister Queen Mary Tudor, and medieval drawings. The rat was actually found in a document by a reader, who must have found it an unwelcome extra. Another unexpected item found in a document was a loaded gun. This was brought to the counter about 8 years ago, by a startled man, and had been left in a metropolitan police file. Fortunately the reader who found it was not a madman ... what damage he could have wrought. There must be a story for crime writers here!