Inspect the various gravestones in the graveyards to find the following references.

Demon door
A gravestone reads "Andy Gay Crushed by a demon door, last words "I swear those things pop up overnight".

Fable
A gravestone reads "Here lies the brother of the notorious Jack, "Fred of Blades".

Florence Nightingale
A gravestone reads "Florence Killed by rabid nightingales".

Legend Of Zelda
Move through a graveyard in Mourningwood and your dog will lead you to a dig location over a grave. Dig there to get a toy sword. Check the gravestone, and it will read "It's dangerous to go alone take this". This is the same phrase the old man in the original Zelda games said when giving you the first sword.

Rabbit and street fight
One grave mentions falling down a rabbit hole another mentions losing a street fight to a rabbit, and a last one mentions a street fight the person in the grave could not win.

Scooby Doo
A gravestone reads, "Mark Church" "And I would have gotten away with it too if it hadn't been for that meddling hero".

The Terminator
A of the gravestones reads "Here lies Arnold, he will not be back".