It sounds very bizarre and I thought that th implication was that he did it deliberately.. I've not read anyting much about Leo but I've never heard of this one.. and I'd assume that he was unlikely to do soemting like put a pen in his mouth when he knew that he was likely to cause serious bleeding. I know he tried to lead as normal a life as possible and not to wrap himself in cotton wool - but Im sure he was sensible mostly about things that might cuase bleeding. Going out riding (for example) might cause a fall and bleeding but it was something that he very likely did for enjoyment.. but I can't see him being careless about sticking pens in his mouth..