What would happen if a relatively small child kills a small animal out of curiosity to see how "dying goes". But it has no idea what death means for the animal...nor, that killing critters is wrong. Parents do it all the time.
I bet that child would grow up and think about it later in life. When I was 14 I was forced to dissect a live frog in science class. The teacher convinced us that the frogs had been "pithed" and thus could feel no pain, but I remember the frogs seeming to wince in reaction to the scalpal piercing the belly. I killed that frog, but not before I saw its beating heart. I think about it sometimes.