The butterfly effect
In the romantic period (19th century), the butterfly was a sign of the hope of resurrection (larva, pupa, butterfly), it also represented the soul freed from all material. I found this nice detail on a large family grave at the Waldfriedhof (cemetery in the woods) in Darmstadt, Germany. On the other side there was a similar metal ball with the symbol of the snake devouring itself.
Please view in full size for the best effect.
Hear the song "Butterfly FX" by the Portugese metal band Moonspell here.