There's always more to learn.

Some medieval portrayals of St. Christopher show him with the head of a dog.

yeahbuhwhat?

I tripped over this fact in a thread about annoying out-of-genre character names in RPGs. It's a reminder that years of study of a period still won't give you a full picture. There's always something new (and possibly very strange) to find out about.

An icon of a saint with the head of a dog would weird out a lot of horror or urban fantasy PCs, and these images could be used directly as handouts in something like WFRP or Werewolf... and that's without actually meeting a priest who looks like an Alsatian under his hood.