I had no idea this was a thing...

 

...and that there was a word for it--marginalia.  So it turns out that the butt trumpet from Monty Python and the Holy Grail was not an original idea.  I did know that those guys--especially Terry Jones--were history buffs and liked to reference historical oddities, though.

Those monks who had to hand copy all those manuscripts sure could be a bunch of dirty buggers.  LOL