It doers not look like anyone can tell where urges originated. it is just first experiences but nothing about reason on why it such reaction took place.

I guess my first time was when I seen the scene in the movie of the japanese general committing harakiri.
Or maybe it was picture of the magic trick where belly gets skewered with sword.
but i still have no clue why I found that erotic way before my puberty or even before before I got to know sexual arousal